Vintage Air Heater Hose Sizing

[Sloonz]

I'm in the process of finishing up the install on my Vintage Air Gen IV SureFit and am wondering what everyone else has done with regards to the heater return line size. The VA side is 5/8" on both heater lines but most SBCs are 3/4 on the water pump. I've found a 5/8" water pump fitting but they're aluminum and I'd rather not use it. Has anyone swapped the water pump fitting to 5/8" and found a steel fitting?

Did some searching and didn't find a definitive answer...