Found info on it over at ls1tech when I had the same question.
Apparently for non drag only cars under abour 450 hp a 3/8 feed and 5/16 return should be one.
They actually said a 5/16 feed was probably ok.
I'm setting mine up the same as yours, using the corvette filter/regulator.
The input to the filter is 5/16 and output and return are 3/8, so I'm just using pipe to an fittings on each to -6 line.
Steve