I have a 4 core Performance Radiator. The thing is big, and stays cool. Their site does ask You the same thing about the cap though. They could tell You why, I don't see much reason, mabey the hoses are different. Seems like the only reason they would ask is because of the overflow tube and where it resides. But who knows.
'84 CJ-7, 6" lift, 33" BFG's, I6, .030 Over, Comp Cam, 400cfm Weber, K&N, T-18, 4 Core, Snorkel, D60 Detroit, Custom CV Driveshaft, 1350 U-Joints, D30 True Trac, Alloy shafts, S.R.S. w/ buggy springs, Custom Folding Shackles and Spring Hinges, Custum Tire Rack, Designed On Board Air, Optima's. Sneaky Jeep Owner #3.