The trans will bolt up but I wonder why you want to change. The 4 speed is a better trans. & 2nd gear is syncronized which you will use for a first anyway. They are not hard to o-haul if it has a problem & the final drive on the highway is the same.
My thoughts exactly... all that work for what?
The SM420 is a rock crusher, a fully sychro 3-speed with an extra low gear for the three times in the next 10 years that you may actually need it... but it's there if you do.
What's the point?
