Help Me Settle A Dispute With Dad

" he did NOTHING but drive it"

Very first things I'd do is look at oil leakage (is the engine worth running as is?) and oil consumption

Then do a compression/ leakdown/ cylinder balance test. Does not sound as if it runs good enough to to the last test.

If compression/ leakdown doesn't look to bad, go through the ignition from stem to stern. (that's the back end, the stem is that funny pointy thing holding the riggin' out in front)

Then yank the carb and clean it out. Check that the EGR valve is not leaking past, stuck open, etc. Consider pulling both valve covers and look for badly worn cam lobes, IE valves not opening or not opening very far.

Oh, one last thing, LOL. It's never a good idea to disagree with your Dad at your age. Even if he is wrong!!! LOL