From what i have heard the 21, 22, 25, 28 are basically the same engine with different strokes, head and sometimes different pistons.
If this is the case then they should all work with the 28 billet flywheel
I know the 28 and 25 shares the same rod and piston except the 28 avs that uses the same piston as the 21 wich is a shorter piston.
If the crank has the same rod journal as the 28/25 and if the stock rod is as long as your 25 rod or the same length as the arc 28 rod you could probably just use the 28 billet rod.