It is all 3/8 from the tank to the pump. It sure seems like a potential bottle neck from the pump to the distribution block to have 5/16. From the distribution block to the carbs the 5/16 is ok. I would bend my own lines but still need to find the right filter. The motor is a 528" Hemi with 494 RWHP, I figured this would be something someone else already figured out.