Quick note on transmissions.

MC21 all models, all years, same transmission

MC28 all models, all years, same transmission.

MC28 has longer 4th, 5th and 6th gears compared to MC21. 1st, 2nd & 3rd are the same ratios.

MC28 gear selector cog heavier and different design to MC21. Smoother change, but MC21 unit more positive.

Both transmissions can be swapped back and forth without problem.