I had the same problem of boiling the fuel out of the Holley 850 DP on a 440. I tried insulating the lines and filter and already had a 1" phenolic spacer. I was told a return line would eliminate the problem. I wasn't sure it would. I bought a Mopar vapor separator and am adding to the mechanical pump. I have 3" headers and ported 915 heads. I was not sure all of this would solve the boiling problem. I drove home from a 15 mile run on a 90*+ day, shut the engine down and lifted the hood and shot the temp with a gun. Carb was 205*, headers were 320. I let the hood open for 2 min and then shot the carb and headers. Carb 160ish and headers 305ish. Closed the hood and waited 5 minutes. Opened hood and shot carb and headers. Carb 190* and headers 280ish. (I didn't write the exact number down, didn't need to) The whole problem for me was the residual head coming from the headers. In order solve the problem I went to two electric fans with two relays and a Daytona Digital Controller that will not only supply the needed air through the radiator, but will continue to "exhaust and cool" the engine compartment for up to 5 minutes. In my case, problem solved and backed up with the vapor separator.