There is no appreciable difference between the 86 and 85 MKII, other than the addition of the 3rd tail light. They are somewhat unique as they were a stop gap until the MKIII hit the market in mid year, so expect some confusion when you go for parts. For simplicity sakes, you can just tell them you have an 85.
The original 5MGE is very durable, but dated. Parts for the engine are readily available for a rebuild. However, there are little or no performance parts still available for the 5MGE, which has led to most people swapping out the engine with a 7MGE or later engine. Not a difficult swap, but you would need the ECU and some wiring harness upgrade.
If you look hard enough, you can still find some 6MGE engines that are drop ins. This is a JDM engine and was never offered in the Supra in the U.S.
The running joke on a 5MGE engine is it comes in to forms, turbo or slow. However, it is very reliable and fairly simple to work on.
As far as things to look for, rust, especially the rear hatch, sunroof, and rear shock towers.
Otherwise, typical stuff you would expect on a high mileage car. Alternators, fuel pumps, starters. The ignitors can be a bit tricky to find. You can still get them new, but they are pricey, $350.00+
...and last but not least, don't forget the irritating clicking noise from the dash. It's part of the automatic temp control and when it begins to fail, it clicks. You can still get a replacement from Toyota.
__________________
|