Trigger Plate Pin(s) Interchangeability

[Smoke-pole]

I currently own 2 Remington long guns, a 742 in .30/06, and an 870 in the LW 20ga 3" Magnum. Not surprisingly, the trigger plate pins for each interchange. I've long suspected that the 870 LW 20's receiver was built on the receiver which went into the 742 semi-autos, but recent research suggests that the 870 LW in 20 Ga Magnums like the one I own may have been built on the 28 ga receiver. But now I'm curious about the receiver dimensions on the full-sized 870s, especially as regards the plate pin lengths and their interchangeability within the family of full-sized 870s.
Also, I bought my 870 LW back in the '90s, used, but in mint condition. It worked fine with the shorter, standard shells, but would jam when using the 3" magnum load. In essence, the gun was shooting a 12 gauge load, and kicked like a mule. I surmised this scenario: upon firing the gun with the 3" shells, the recoil drove the gun rearward while the shells in the magazine stayed (momentarily) in the same location ( kinda like when a magician snatches a tablecloth from under a table set with dishes and silverware), creating space between the magazined shell's base and the forward end of the shell latch. A split second later when the gun returned to the pre-fired, shouldered position it combined force with the magazine spring tension which overpowered the shell latch, allowing the magazined shell to enter the receiver before the bolt ever got unlocked. I was able to continue hunting that day after removing the magazine cap, spring and follower, thus working the jammed shell back into the magazine. At any rate, I replaced the latches and so far it's working OK. But given the fact that Remington discontinued its production (unless I'm grossly mis-informed) I'm left to wonder if complaints from other owners led to the gun's demise. I would appreciate any insight that you guys can provide.