I just went thru this with a numbers matching 1970 Roadrunner that I put a 511ci engine in with 10.5 comp. I wasn't about to cut or change the core support. So I went with a griffin exact fit 2 core that was 26" wide. I made some aluminum brackets that bolted to the original radiator holes and spread out to mount the 26" radiator to. My thought was, I'm gaining additional water capacity and additional cooling contact surface to dissipate heat. I also had to use the Hayden short muscle car HD clutch fan clutch and a original Mopar fan. There's no sign of heating issues in the hottest of summer days in California (95 to 100 and it runs 180-185. I cant say it's ever gotten hotter than that.