what year for small rear main bearing?

Anyone know what year the rear main bearing changed from a large cap to a small? I bought a 72 dodge truck 318 with a 727 trans, but I think that at some point the engine may have been changed out, so I am not sure exactly what I have. I am trying to buy an oil pan but a '72 has the large rear main bearing and mine has a small main bearing. It has a two piece rear main seal, small rear main cap, 4 barrel carberrator and electronic ignition, it is a small block V8. I put it in my 66 plymouth belevedere so I need a mid sump oil pan but the engine came with an oil pan with a rear sump so I could not bolt it up. A '72 318 challenger oil pan bolts up everywhere but the rear main cap where I have about an inch gap so I can not get a seal.

rear main seal

A 318 and 340 passenger car oil pan will work. 1967 up.

need an oil pan

the rear main cap opening is too large on the 60s models that I have tried and the 72. I also cannot find the engine casing number to correlate anywhere. We have checked and the 318 truck and cars use the same oil pan/gasket and that does not bolt up to the rear main on this engine

Could be mistaken here- but if I'm reading the post right it sounds like the gap around the rear main is because he's trying to use a 318/340 pan on a 360. All of them I ever worked on were like that- 360 pans gad larger radius. Feel free to correct me if I'm wrong or missing something...