Hey, why dont you just get a 69 428 with stock 390 hp under rated of course, more like 410 hp and run that. that way you could drive it most of the time trouble free and still run well into the low 12's and 13's. I have one in a 66 gto and it will pull high 11's in the quarter and it is a huge car! All i did was put in a nice roller cam set up ported heads a pair of slicks, and kept the rest stock. My car has a 4 sp though so that makes a huge difference. good luck, and if you run nitrous, rebuild the bottem end or it will blow. trust me, been there done that.