Yeah I had been looking around on the Internet, but to no avail. I believe ours is 3.5" and that a 4.0" would drive it nicely. Keeping in mind that pushing the pump faster will increase the flow rate and possibly PSI. I'm interested in testing. If you can't find something in the Junk yard, maybe someone with a 3D printer could do an ABS print for testing. As for radiators, they are available in the custom / universal styles. Universal would require some custom bracketing to keep the accumulator and lower cooling lines in place. Proper custom ones should be able to have those items taken into account like the OEM versions, though I'd expect 3x the price of an OEM.