1989-1992 LX 5.0 Coupes are in demand these days.
It may be a little hard to come by one in good shape. As far as reliability according to the data history they are 4 and 5 star car's. In otherwords, reliability is awesome. You are always gonna find some cars that are problematic, but you have to look at how they were taken care of or driven.
It would appear that you are looking at the MAF equipped cars, the 1987-1988 (non CA) 5.0's were SD "Speed Density" equipped and outperform the MAF equipped cars stock for stock by a couple tenths in the 1/4. The rating on the 1987-1992 5.0's is 225hp@4200rpm, 300lb@3600rpm. I don't know as those numbers are all accurate, though. The 1987-1988 cars run quicker, only the 1987 was ever actually rated. They just carried the numbers over year to year after that. In 1993 Ford re-rated the 5.0's at 205hp, and 285lb. Truth be told, the 93's got cast hypereutic pistons, and a crappy computer. Ford said the re-rating had nothing to do with actual output, just a different way of rating (average vs best output). Don't believe it. That's a crock. The 5.0's all dyno pretty damn close year to year. The truth is the MAF cars do not make 225hp and 300lb. Course that's all theory and no documentation exists to support that information. The only thing you can back it up with is 1/4 mile times.
Speaking of which
1987-1988 LX Coupe 14.3/14.7
1989-1992 LX Coupe 14.5/14.9
Those are pretty good base estimates T-5 vs AOD.
I know, I know, it's a GTech run, but my out of tune 87GT Hatch with 145k on the clock just pulled a 14.19@103.8 with the mods in my sig, and a plugged up K&N. The time should be really accurate, but the Gtech reads high by 3-4mph trap speed.
Now down to the nitty gritty.
Auto's- Equipped with the AOD tranny and auto 5.0 will run a good 3-4 tenths slower in the 1/4 mile. They can be modded to do much better, but they are not fast by any means in stock form. They need a good converter, a shift kit, and some low rear gears.
Manual- The Borg Warner T-5 manual's have been given a reputation of being weak. Whether or not that's actually true is another story. I think they are a solid tranny, put an aftermarket shifter on them and they'll go a long time, and they'll handle quite a bit of power. They run 3-4 tenths quicker in the 1/4 vs the auto, and they can benefit another 3 tenths easy with some 3.73/4.10 rear gears.
The 5.0 will go about 120k before it begins to show age, mine has a 145k and it's still running strong, so 120 isn't by any means an exact number.
Most drivetrain parts will never give you a hassle on the cars. There is so much difference between optional packages and models that you really have to shoot an idea of what you are looking for exactly in a car before I can say which one's you should be looking at.
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1987 GT 5spd.
D&D Performance "Z" spec T-5
Dynomax 2.5" Super Turbo system
BBK 2 1/2" H-pipe with cats