If you dont want to go in the motor do not use the 278's. Will not work on stock motor as I found out the hard way. WAY to much duration and lift for stock stuff. Iam having to flycut pistons, port heads just to use the cams. They are way big. They sound ***** sweet though. I think your on the right track. Due the exhaust now. Dont waste your money on shorties, buy long tubes, due the TC, and the gears, youy will love. Good luck.
Check mt thread out called, what comp's 278 due to stock motor. You will see what happens to the pistons.