Fuel piping question

I don't see what good the -10 lines will do at the beginning of the system. -8 is way more than big enough.

Normally the regulator should be as close to the carburetor as possible. If you get a regulator with one "in" port , one "return" port, and at least two "out" ports you can eliminate the dual feed carburetor lines/adapters by running a line from each "out" port on the regulator to the two fuel bowls. The two lines from the regulator to the carb bowls can be -6 which is again way more than big enough.