I think the '95 5.0 would have been in an Exploder or F-150. The last year was '94 for the 302 in Mustangs. I think 90 was the last year for forged pistons in the Mustangs. Actually it doesn't matter because if it's rebuilt the parts in the motor are whatever the builder decided to put in there. Could be really great or absolute crap. Depends on how much you trust the guy's expertise and honesty.
You said your power goals are 350-400. I assume it's a street build? Do you want it to be naturally aspirated or is forced induction ok? If you buy someone's rebuilt 302 you will have to change a lot to make 350-400 NA (probably heads, cam, intake, carb, but maybe also pistons). I would just buy a core and plan to build from scratch in that case. I would definitely do a 347 stroker to get that kind of power and make it fun to drive on the street. You could maybe buy the 302 and add a blower to get yourself there - depends on how good the internals are. They put those little Paxton blowers on some of the Shelbys - that would be fun to have a modernized version of that drivetrain.