The heater cores from early years are little different than the new ones.
Spacing of heater tubes and the thickness of the core.
Newer heater core can be made to work with carbide cutter, but treasure hunting & finding a NOS one is so much fun.
I think I need Laura Croft on my treasure hunting team.
67 Gladiator 15K J3000 AMC 327, PTO, 35" BFG's
69 Jeepster 8701 convertible
80 Honcho Sportside
82 CJ-8 75K org SR decals
82 Cheroeke Laredo 24K
83 CJ-8 50K 401, ARB60's, F&R Winch, 38"
84 CJ-7 38K Garnet Int., Jeep 8274 winch
84 CJ-8 mud Scrambler
87 J 20 36K smooth alum camper & boat rack.