I'm setting up my fuel system for my 565 blower motor. the fuel pump is a mallory comp 250 that has a fuel return fitting. the regulator is an aeromotive that also has a fuel return fitting. which return should I use & which one should I cap off ? Is returning to the filter head okay ?

The only way the fuel pump would have a return is if it had a built in regulator. Call mallory and ask them for the plug for the regulator adjustor. I would use the return on the aeromotive regulator as it will be closer to the carb / efi. Mallory made it clear to me that the regulators may fight each other and I needed the plug to disable the regulator in the pump.

the description said the pump has a 8AN inlet/outlet, 8AN bypass and 1/4'' NPT air bleed

The separate regulator is generally where the return line comes from...I run a aero a-1000 and their carb regulator, has a #8 return off of that...