Full and mid-size cars with 302 and 351W but make sure they don't have the FMX (cast iron case - aluminum bell and tail housings).
I like the pan fill with the case mount bell housing but there are clearance problems on some cars and with headers with the case mount bells. There is the added expense of the new valve body, converter and bell housing to make the C5 into a C4. aside from those pieces if you get a C5 from most any full size car it will have the five clutch drums and will take less internal mods to make it a durable transmission.
What are you planning to put in front of it? How much HP will be under the control of the tranny?
Paul