Yes with your assistance and engine no being 1904 I think it should be the earlier one. I take it has the vacuum advance on the top, not on the side as per my photo. So is it an easy swap out ?
Well, we are talking here about two different things:
a) the distributor
b) the throttle housing (Venturi housing) in front of your intake manifold.
Both should match.
a) Your distributor appears to be correct (see (and read) my post above)
b) your throttle housing?
Don't know which one you have, you did not show us.....
For a correct 127981-20-001904 engine yours should look like the one on the pic (not mine) attached.
Regards,
Achim