AS stated above it really depends on what you are looking for in donor parts. If the 85 was reasonable (read cheap) enough, I wouldn't see any harm in picking it up. The 5.0 in 85 would be EFI and an AOD was also available. Rear and front ends essentially the same, body parts, meh, depends. Interior obviously no.
If it was me, and it has been me in the past, I would primarily search within your generation. That will give you interior and body parts. Like stated above engine/transmission donor of 94-96 5.8/E4OD would be most ideal. If you pursue this route just know there may/will be some wiring differences.
A positive for the 85 donor is it MAY have the older style steering knuckles which would allow for a T-Bird caliper brake upgrade on the cheap as you'd have the only "hard" part and all the other you'd be buying new anyway.
hth and welcome aboard.
tim