I am using the MegaSquirt n Spark - Extra system to control both fuel injection and ignition timing on my normally aspirated 1987 MR2. (Edit: Now Turbocharged!) I have built a system that is very nearly “plug n play.” It uses the completely stock ignition system and engine harness. The only wiring changes inside the engine compartment involve plugging three wires into an existing connector.
You can read about it here: MegaSquirt Install
The system has been used on 85-86 Mr2s, 87 Corolla with the 4age and VAST ignition system, and a '88 22re pickup truck. I don't believe this system will work on 88-89 NA or SC Mk1s -- they have a slightly different ignition system. It definitely won't work with 4ages that came with the ESA ignition system, which is just about any Map-based 4age.
Check out www.diyautotune.com for MS kits and assembled units. He's a Mr2oc.com board sponsor and MK1 MR2 owner.