2-piper, that's interesting - I also have a late H grade Lefever assembled by Ithaca with an Infallible trigger. The serial number is 71xxx. As you know, it is difficult to put an exact date on the sideplate Lefevers, but it could have been made as late as 1919. Like you, I can't be sure the trigger was on the gun when it left the factory, but I suspect that to be the case.

The forend serial number on my gun doesn't match the frame and barrel and appears to be for a DS model.