Ideally, the return line should have been at the end of second carb, for a good flow through and bring cooler gas into the carbs. But we couldn't find a way to run a line from the end of the second carb, so we installed the tee on the fuel supply line to the first carb. It seems unattractive in the photo (below) but it was relatively out of sight and surprisingly worked quite well. I think it was a Ford T valve, 3mm flow with 1mm T.... The return line allowed for pressure relief from the excessive heat when the car was still (or turned off) after running hard, and was all that was needed.