Along with the items that you pointed out, the sights, both front and rear are from a later model
I've never seen a serial number in that location only on the right rear aft of the selector and the font looks wrong but "never say never"
The later style H&R engraving is pretty definitive and the receiver finish does not match the rest of the gun. Other than it's probably built from parts like you suggest I can't explain that one.
That dealer has some interesting negative feedback about the honesty of his descriptions that you should also take into consideration
I would run, not walk, away from that one. There are nicer GENUINE early guns to be had for a lot less money