Help me build my 360!

you could have the engine internally balanced and get a neutral balncer and flexplate....

but if you are on budget...stay with the external balance and flexplate... mallory metal get costly .....

you could ask the machine shop for a quote to internal balance verus external and see how that works out....if the money saved will pay for other things.

pistons are a very good choice...
as far as carb i would use a holley but that is my choice...
cam....look at the comp or lunati 904 lifter cams...

heads wise....might want to take a look at the engine quest magnums with LA bolt pattern....also Indy and RHS have a new cast iron head out...