psmith1954,
Another impediment to using the SM420 transmission in place of the '34 non-synchro "crashbox" is the difference in the front main shaft bearing retainers used on the different transmissions.
Your original '34 will have an opening in the bell housing for the 4-3/16" diameter front main bearing retainer on the "crashbox".
The SM420 front main bearing retainer has a larger 4-11/16" diameter bearing retainer that won't just slide into place into the existing bell housing hole without opening that up to match the larger diameter.
If you do go the route of opening up that hole, extra attention is needed to make sure the change keeps the SM420 input shaft alignment correct to the crankshaft bearing where you input shaft will ride.
While others come along to chime in with more info, check out this
earlier conversation about the conversion you are talking about.
Dan
