Rich, they pull fine and right round to flat out in top (stock '28 gearing is 44/15 so that's only about 115mph for 11,500rpm in top), just with no real gusto.

If it's running stock pipes and a stock airbox it's almost certainly a stock motor which someone has tried to jet to run better with the powervalves set wrongly.

Billy's '21 was exactly the same, stock motor, stock pipes, stock airbox, massive mainjets, 42 slows and the power valves lined up with the TPS plugged in.
I'd check the power jets are still in place, check the slows are 38's and swap the main jets back to stock (140's).
Then take it for a spin, I'd know straight away if I was going in the right direction, a stock '28 is almost unbelieveably smooth and tractable.

Note this is what I'd do, I might be wrong....

And this is walking right on the edge of discussing jetting in General so I'll leave it at that.
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