I'm restoring my Mk II kodiak heater and I've been checking out my heater core. I think my original one is ok, but I've been preemptively looking for replacement cores. My original core is 7.875 x 6 x 2.5 I found vista-pro ready-aire 399007, which is for a 1964 Ford falcon/ Mercury Comet, which is measures 8 x 6 x 2.5, so it is only 1/8" longer than the original. It even has the pipes in the correct location as well. Knowing there is some degree of slop in the case, I'm guessing that extra 1/8" won't be significant. I haven't bought one and know nothing about be quality, but I figured I'd pass this along in case it helps anyone.