Got the amp working easy enough and sounds pretty decent- https://www.youtube.com/watch?v=bEtvu4ldFts but didn't have a lot of hope for the original motor after retensioning the brushes still not able to get continuity and the commutator looked burned, so decided to repower with a Mabuchi RC280 RC car motor, turns out these are just a purrfect 24MM diameter case and 2.0mm shaft size compared to the original-
The resulting speed achieved was ~22-1/2 RPM
so I thought about it for a day or two while I have been waiting for a couple other motor choices, ~$2-$3 free shipping from China!
But tonight I thought about ways to increase the speed with a sleeve over the motor shaft and picked a piece of PVC ~18ga wire insulation which got me close to the right speed, but adding a piece of shrink tubing over that made it just about the right speed at the top of the range
https://www.youtube.com/watch?v=85gdEytzZac The case cleaned up quite a bit with my favorite lanolin hand cleaner, a nice brush and a moist rag.
PWM controller and lower voltage motors coming soon, this one was advertised as "3, 6, 9, 12V . . . " 17,000 rpm . . .YMMV
The resulting speed achieved was ~22-1/2 RPM

But tonight I thought about ways to increase the speed with a sleeve over the motor shaft and picked a piece of PVC ~18ga wire insulation which got me close to the right speed, but adding a piece of shrink tubing over that made it just about the right speed at the top of the range

PWM controller and lower voltage motors coming soon, this one was advertised as "3, 6, 9, 12V . . . " 17,000 rpm . . .YMMV