[mytopless68gal']

Yes, a 390 from a t-bird should work just fine. A 390 is a very nice engine, (it's what I have in my 68 gal' convertible, and it's a real work horse), but if you're wanting a really fast engine, you may want to look into a big bore, short stroke engine, like the 427,428, or 429 cobrajets. You will pay quite a premium for these engines however, as they are very sought after. (Mainly used in the various Shelby Cobras)