Yes, if you are going to be reusing parts then the build goes down a different path. Sounds like the short block will be all new parts though?
Yes, I would be starting from scratch on the short block unless I stumble onto a good deal used. I do like the idea of going bigger with the engine and being easier on parts. Lower RPM etc. I race a lot and longevity is a requirement.
Aluminum block lets you go 4.500 piston which is a good size to use since lots of choices for rings. I'd go with a 540 if you use an internal oil pickup, or a 572 if you are already set up for external oiling. The weight reduction from the block plus the extra torque from a bigger short block should both help the car get moving.
I had a customer step up from a 505 to a 572 last year and the extra torque scared the heck out of him. First time at the track with the new motor the car lifted the front tires about 3 feet and that freaked him out. It looked cooler than hell but his eyes were big when he got back to the pits! He ended up swapping out the 727 for a Glide and that helped to settle the car down. Also made it more consistent.
