Have you checked out late 80s Mustangs as possible head/engine donors?
Anyway, since the original engine was FI, you should have all the parts/wiring/sensors you need. Set them side by side and check it out - if there is a hole and gear to run your distrib, you should be good to go!
Good luck
PS: FWIW, I believe the stang 2.3s didnt get 8 plugs until 1993: (Edit: and I'd be wrong about that - 91 to 93, apparently)
http://www.allfordmustangs.com/forums/2-3l-talk/87135-1993-mustang-2-3l-why-8-spark-plugs.html
A relevant thread (though it kinda got hijacked in the latter half) pretty much gives the thumbs up to older 4-plug head on newer block:
http://www.ford-trucks.com/forums/595513-help-with-engine-swap-2-3-4-plug-to-2-3-8-plug.html
Lastly, a maybe foolish thought - what, if you are able to mount your distributor on the 91 block/head (and it will drive the 91 oil pump) would happen if you simply connected 4 of the 8 plugs (1 per cylinder, natch) and left the others as dummies? Apparently the later intakes covered up the distributor area, but if you're going to be reusing your 86 intake anyway...)