"as far as i know all a series flywheels are interchangeable, the difference is the weight.

even on a 63a transmission the same flywheel works."

I would lighten it first..its so inexpensive like $100 and the difference is significant.

Also B210sleeper is right the A12 flywheel is slightly heavier, but all a series flys will fit the a series range of motors.
What you do have to look for is that the clutch packs for the 63a gearboxes will be different due to the bigger l series sized input shafts than the 53a and 60a.
Bigger clutch plates also have bigger pressure plates which fit onto any a series flywheel dowel pattern provided you know which one to order.
Anyway when machining the flywheel, make sure you machine the friction face flat as stock flys have a small ridge to accomodate the small clutch plate.