I use to love doin ground ups. I would go with the 3.55's cause the big block can't rev like the small block. Also make sure to weld in sub frame connectors so you don't twist the body or rip the rear from the body. Are you going with full race auto trans, turbo 400 with shift kit or a stick? Enjoy the build and don't rush cause you're getting inpatient. You'll be happier in the long run if you take your time and do it right.

BC