I need a heater core with 2 different hose sizes for my 68 Barracuda

i had sent you a pm about the 2 i had, looked them up , 1 is made for a 73 to 76 duster or dart, the other is made for a 70 to 76 duster or dart, both have 5/8 on one side and 1/2 on the other, ebay is covered up with photos of heater cores with 2 different size tubes leaving heater core and would require 2 size hoses, is what my 225 74 duster started with,only reason i changed core was original one leaking and it also had 2 different size on the 71 challenger 318 ,that i put in ,so i kept mine as is, and i it heats better than the 2011 dakota or 2008 ram i have. Could someone have put a newer motor like 70 or newer and changed heater core to match? or maybe the water pump or intake may have been changed,after all, we are talking about a 50 year old car.