I agree with the suggestion to run carfax on it. See if the car itself checks out okay, regardless of drivetrain. Dont worry about the drivetrain, just check out the car first.
As far as the drivetrain. If the car is a '85 the drivetrain has been converted. This is not uncommon at all. Even if you think it looks factory it doesnt have to have been done at GM, besides it couldnt have been, '85s did not come with that engine. My brother had an '86 that the body was rotting away, so we took the drivetrain and put it in a '84 we had with a good body. You cannot tell that the motor did not come in there. If the care is taken to do everything right it will look right. There are a few other conversions around here that I know of also that look right. One that doesnt
Could be whole drivetrain, or maybe its just the bolt ons on a '85 block?? Look underneath and see if the tranny tag on the passenger side tailshaft says BQ (84/85) or BRF (86/87). Check for the sticker in the trunk and see if you can get any info from the option codes, should have vin at the top of this sticker too (I think). Definately check the vin #. I think its the 8th number (correct me if Im wrong) that designates engine. #9 was the code for the turbo engine in 84/85 and #7 was turbo engine for 86/87. Nothing wrong with a good conversion. If its a pretty clean car might be worth picking up. Not a bad price. Only real question with conversions is................where did the drivetrain come from??
Hopefully not out of a TR that came up missing. May not have been acquired this way, but who knows?? I have a '87 drivetrain from a burnt up TR I bought from a auction. I have gathered most of my hotair engines and parts from guys that the cars were wrecked. Just check out all you can and then decide. Heck, its hard to make the call even if the drivetrain was hot. Probably would be better if it fell back into the hands of a caring TurboBuick guy/gal rather than just getting dogged or trashed out on the streets
. My 2cents
P.S. oh, and yes the easiest way to tell if it is newer than 85 is if it has a 3rd brake light. Grilles are also different, etc. Not that these things cant be changed or added...