firstly, he needs to realize that the GMC core he's judging by is likely a replacement, I would expect most 5-7 cores have been replaced by now .... for the deluxe version heater I would really doubt there was any differences at all between Chev and GMC, they were both made by Harrison .... but there is a tube size difference between truck and car heaters, I suppose it's marginally possible the car core was used on GMCs
Bill
