yeah Fieros are GREAT little cars, the best ones to get (if you can find em) is the 88 model with the lotus suspensions. my dad had a 88 Formula coupe (basically the GT but with the base model's bodywork). the great thing about those cars is almost ANY front drive GM drivetrain will drop in there as the Fiero's rear end was based on early 80s front drive platform and the front end was believe it or not chevrolet chevette/pontiac 1000
. sure you can put V8s like the a LT1 or a LS series V8 (ls1, ls2, ls3, etc). but I seen cars with mid 80s and up caddy motors and northstars. all you really need is aftermarket half shafts to handle the the torque those motors put out (you can retain the stock transmissions, just swap the Fiero half shafts for the tougher ones). there is a online store that sells stuff like that for those cars, go here:
http://www.fierostore.com/ 
.
edit that link is for stock Fiero parts, i am not sure if they carry the beefier halfshafts or not. but if they do cool, if not, i am sure there are places out there that do, just do a search for 'Fiero V8 conversion parts' and just get the shafts
.