Hi, there is a '70/'71 engine/transmission for sale nearby, would any of the cases, transmission parts etc. be compatible with my 1972?
Thanks.

The "tech library" here has parts lists for those bikes. You could compare them. Also, partzilla does product fitment across the years for parts.

The 1971 DT1E Service Manual in the Tech Library has a Service Bulletin in the back that describes the different gear design and interchange for the earlier models.

I'm late to the party as usual but according to partzilla & my own thinking back to the day. "70 & "71 have the early trans where the 4th 5th selector is part of the drum. I've mixed n matched everything possible over 50+ years but be very careful. The early trans cases don't make provision for the 4th 5th delector shaft as isn't necessary. As a complete set with drum & its selector it should swap in to your "72. Only other issue is the early ones has coarse tooth gears but might've gone to fine by "71. I used to blow 3rd gear big wheel to pieces on the early box but that was doing pretty hard out mx riding & clutchless changes up n down. Clutch--what's a clutch lol. "70 & "71 partzilla links below.
photos.app.goo.gl/bJRYMSpjE9VoaiFY6
www.partzilla.com/catalog/yamaha/motorcycle/1970/dt1c/shifter-a
www.partzilla.com/catalog/yamaha/motorcycle/1971/dt1e/shifter-a
 

Thanks.