I've converted a few Small frame Smiths to 32 H&R Mag. Just about the simplest re-chamber that can be done. So little material is removed it's akin to opening chamber throats to proper size.
The reamer can be turned by hand with a T handle.
In I frame and new I frames, the barrel/cyl gap will be sufficient to compensate for bullets a few thousandths longer than the chambers. Or worse case scenario, bullets need a few thousandths slight deeper seating; either reloads or running factory ammo thru the seating die.
The dash 1 .32s are J frames with about 1/8" spare length in the chambers. There's no strength differences between Post war I frames and J frames.
The rear face of the cyl nor headspace is an issue. Just don't ream deep enough to recess the case rims.
This is my first re-chamber to 32 H&R Mag, a 4" J frame Model 30-1, 1966 vintage:
Photo by James J. Carter
Others have been snubby Model 30 New I frames.