My 360 build.

good find and a
good question on the valve reliefs
What pistons?
too much deck clearance with that gasket and -20
use a .028 gasket _.020 deck clearance gives you .048 which is about max what you want for quench or .038 with your .010- you are in the ballpark
does not Edelbrock have several choices of cc's?
you want the larger of the closed chamber type- not the open chamber with the .100 recess LA stock style