If it's an unmolested '67 it'll be a Synchro Mesh 420, if out of a '68 or later it's the SM465. I believe the transitional gearing is different -- the earlier tranny starting out even lower. Both are 1:1 in 4th, of course. Jeep and Toyota guys seem to think Muncie 420s are neater than sliced bread; I think it's a fit thing. The 465 is slightly longer, and if you have a '72, maybe you should look for a '68 or later SM465 if you want easy bolt-up capability. I know a '72 465 fit on my truck ['68] like it was made for it.
