This is a translation made from Patriks homepage, with his approval. 
I (Widde) has only translated this text so close to the original text as I could.

T16-Engines in  SAAB 900 84-93 is equipped with an ordinary distributor. This kind of ignition works as long as the engine remains stock (no extreme tuning) and the engine is in good working condition (all mechanical parts working at their best).

Why exchange to DI?
Well, distributor based ignition is rather primitive, the only adjustable solution in a turbo application is a mechanical ignition setting through vacuum from the intake. The distributor switches between two settings depending on load of the engine, nothing else. A working distributor is then really important.

DI makes the work better (to say the least), and without many moving parts. The DI uses the "ignition point" sensor, MAP sensor and the fuel data from the LH system to calculate the most optimal ignition. The spark is also a lot stronger, aprox. 40000 volts. With these conditions the combustion is better and the engine is less inclined to knock. This is what we want! And now the conditions for tuning is a whole lot better.

Parts:
The DI-system is taken from a SAAB 9000 CD Turbo 2.0 -88, there are the DI separated from the APC, which makes the conversion rather easy. This version of DI and APC is called DI+APC, in contrary to the DI/APC which is made from -89, there the DI and APC is integrated in one box.

The complete DI-system consist of the following parts:
1. A complete DI-cable trunk.
2. DI ECU, looks like a APC ECU but it says DI on the box.
3. MAP sensor (Manifold Air Pressure), DI needs to know the pressure to know the load of the engine.
4. "Ignition point" Sensor, is mounted on the Oil pump cover. Also named EZK, hall effect sensor
5. DI-shutter wheel, is mounted inside the crankshaft pulley, which gives a signal to the "ignition point" sensor.
6. DI-cassette, the part that goes into the cylinder head

And the following:
1. Oil pump lid with place for a "ignition point" sensor.
2. EZK- crankshaft pulley from a 900i 16v with EZK ignition system

And you need to change:
1. Sparkplugs, the regular plugs are not compatible. You need NGK BCPR7ES11. 
R is for resistance.
11 is for 1.1mm spark gap   

Conversion:
The "tricky" parts in the conversion job is the mounting of the "ignition point" sensor and the shutter wheel. To mount the "ignition point" sensor you'll need to exchange the Oil pump cover to a cover with a EZK "ignition point" sensor already mounted. This Sensor can't be fitted on a ordinary cover.
The Oil pump cover with the "ignition point" sensor can be taken from any SAAB with a B202 engine, equipped with either DI or EZK ignition. The only thing that differs between "ignition point" sensor is the cable length and the contact.

From the following SAABs can the Oil pump, "ignition point" sensor and shutter wheel be taken:

- SAAB 900i 16v N/A,-88/89(?) to -93 (Oil pump lid and "ignition point" sensor )
- SAAB 9000 CD 2.0 Turbo -88, 9000 Turbo 2.0 -89, to -92 (Oil pump lid, DI-shutter wheel and "ignition point")
- SAAB 9000i 2.0 16v,-88/89(?) to -92 (Oil pump lid and "ignition point" sensor)

When it comes to the Shutter wheel it gets a little bit harder. The Crankshaft pulleys are not the same between 900 and 9000. The DI-shutter wheel needs to be mounted on the 900 crankshaft pulley. But does the DI-shutter wheel "bolt-on" to the crankshaft pulley? No! You need to do some mods and "presto" you got a DI-shutter wheel to a 900.

The Crankshaft pulley MOD
How to...
..Well start with the EZK-crankshaft pulley from a 900i 16v with EZK-ignition.
This Pulley needs to be machined a bit, because the DI-shutter wheel has got a slightly smaller internal diameter than the 900 EZK-shutter wheel. To get the DI-shutter wheel to be mounted you need to modify the holes on it. The spacing between the holes are the same between the shutter wheels. The DI-shutter wheel is aprox 1mm lower than the EZK-shutter wheel, so you need to add spacers under the shutter wheel so it is placed at the correct height from the "ignition point" sensor.

When all mods are done, just put it all together. Do not forget "nut lock" fluid.

The Oil pump lid
It's a bolt-on. just change it.

The job
It's a step by step job:
1. verify the cable trunk
2. mount the cable trunk from the engine room into the car. One solution is to follow the LH cable trunk.
3. connect the DI-cable trunk into the car (Get the SAAB workshop manual of the DI/APC system, the manual contains the wiring diagram)

You doesn't need to connect the pressure signal from DI to the APC. If you got a APC from a SAAB 9000 CD turbo then you could connect this signal.
4. Connect the MAP sensor into the engine by a T-connector. The MAP sensor can be mounted anywhere that the cable trunk permits.
5. Mount the DI ECU at a good location
6. Disconnect the distributor, This is important! We doesn't want the ignition coil, distributor, and included parts to interfere with the DI system
7. Mount the new sparkplugs (resistance type plugs)
8. connect all electric parts (MAP sensor, Crankshaft sensor and ECU)
9. Verify that the Distributor and all parts are disconnected and recheck the sparkplugs

If the wrong kind of plugs are fitted the DI-cassette will break! The cassette is not reparable! New Cassette is then needed. NOT CHEAP.

10. mount and connect the DI-cassette.

The start-up
Turn the key, start the engine, listen to the music, enjoy.
Congrats the engine is now converted to DI.

Hint!

If the local car control department is a little "picky" about the conversion. Leave the distributor and just reconnect it and exchange the plugs, when the car needs to be checked.

Finishing up
If wanted you can just remove the distributor and exchange it with a plug. This plug is avaible from any SAAB with DI or Trionic control system. Go to the nearest junkyard and get one. 

Pictures
Oil pump lid with a "ignition point" sensor from a 900 with EZK


Stock EZK-Crank pulley


Modified EZK-Crank pulley


EZK-Crank pulley and DI-Crank pulley


DI- and EZK-shutter wheel


This is how much the EZK-Crank pulley needs to be machined


This is how much the holes needs to be modified


Cables with the DI-box on the Left and a APC-box on the right


MAP sensor to the DI system

DI-cassette fitted


Mounting the cables inside the car


The distributor plug


The old Oil pump lid with the crankshaft pulley