[BLACK85GT]

Yes the 87 heads will fit, and are better because they are the heads used in the F150 trucks so they are suppose to flow better.(always check clearance to pistons of course).
Just remember if you buy a rebuilt block from a retailer it has allready been bored so future rebuilds might not be possible. I did that once, engine lasted about a year, now i took it apart and its bored .40 over so boring it more is not an option for me.
I am considering the Ford Racing Production short block. Its a complete Brand New roller block and the parts are all Brand New. Cost is about $1,250. Thats about $400 more than a rebuild but it is not bored so you can rebuild in the future.
Plus I like the fact that Ford put it together and you know exactly what you have.
Also, the heads will be more effective if you get a better intake. They are rather cheap. You can pick up a used Edelbrock Performer for about $75 or less. Remember the better heads need to breathe better. If you get one that is too tall though you will have hood clearance problems(Performer RPM is too tall for stock hood).(I have an 83 gt hood and just cut a hole under the hood scoop). Hope this helps. Any other questions let me know cause i am going thru the same thing.