I found a .030 over 350 with flat tops in my uncles garage, that had been put together 15 + years ago but never run. Was wondering if I just disassembled and cleaned would it b goo as new?

Personally I'd take it apart and check everything. As long as you carefully mark where each piece came from (bearings, lifters etc) you can reuse the parts. You might have to re-scuff the cylinder bores to take out rust. Retorque everything. You also have the options to take the heads to someone experienced and have them just clean up the intake and exhaust ports, maybe drop in a mild cam, and dual roller timing chain.... :)