Well, for a TRUE XM177 (not 177E1) the receiver is a good bit different. The carry handle is attached, there is no forward assist, receiver guards around the mag release, and brass deflector is shaped differently.
See this pic for a proper 177 (Technically a GAU5A/A [the longer barrel gives it away], but I digress):
I like early Vietnam loadouts especially Airforce Combat Controllers, so I've gotta have the original, non E-1 177.
But, I'm just splitting hairs here, lol...
With the Vietnam players, they are a stickler for details. Worse than WW2 players.
Technically, there were several different models and variations in the GAU5/XM177 series, but still, the TM has a FEW key features wrong. You can get away with the forward assist, as the E1 and a few other models have it, but the receiver shape and brass deflector are a dead giveaway.
Now, to Senor, the gun is good as just a gun, don't get me wrong. It's just the silly perfectionist in me that is looking for a proper reenactment weapon. For your purposes, it should be great.
Plan on upgrading it, or do you want it to last forever, lol?
EDIT: Just saw the "upgrade the motor" plan, so nevermind. Fire it first, the ROF with an 8.4 should be very decent. You may not even want to upgrade.