I'm no expert but believe I'd jump on the Valiant with a V8 if you're wanting to go V8 on the cheap - already has a V8 K frame, discs, and might have an 8 & 1/4 rear end. You ought to be able to recoup some of your investment by selling off the rest of the parts - interior, instrument cluster, useable sheetmetal, etc. Just my 2c