What do you call this?Actually, it doesn't have a carrier release latch, so I don't believe it is for a semi. It also looks to have the flextab cuts, which I think are only present on 870's.
I assume you are talking about the first picture posted in the link you attached, before the after market lifter was installed? The trigger group is the same as what the OP posted. The only difference is the size of the stock bolt release lug. I have seen some Remingtons with this bigger lug, but I dont know if they are a factory. Their are a slew of aftermarket parts for these guns, bigger lugs being one of them.