"You have to cut the brass to length, shave the base from .058" to .035" and deepen the primer pocket. "
The standard procedure for thinning a rim under similar circumstances is to do it from the front, not the base, for obvious reasons. The recommended case to use is the .45 Auto Rim, not .45 Colt or Schofield, and the recommended final case rim thickness is 0.039". The recommended trimmed case length is 0.886". .45 ACP dies can be used to reload the reformed cases. However, there may be some problems with the strength of the thinned rim while full-length resizing and priming. I might consider using a manual Lee Loader for resizing and priming for that reason. It might also be a problem in finding a usable shell holder, I don't know about that.
Thinning the rim in the proper way is best done with a small lathe. Although some say it can be done with a drill press and a file, I use a lathe. Fairly easily done (if you have access to a lathe). I have thinned many hundreds of case rims that way.