Well I have a bit of knowledge when it comes to the 833's and 833OD's.
There were 3 different sizes of bearing retainers used on the 833's.
The smallest was the 4 1/4, and was generally used on the earlier trannies, and the 23 spline 833 from 65-87 and was used on SB and 383/400 engine cars.
Then there was the bigger 4 5/8 bearing retainer. This was mainly used on the 18 spline "Hemi" tranny. This tranny was used on most 440/426 applications from 65-71.
Then when they went to the 833 OD tranny, which was the exact same casting as the earlier trannies but was generally an aluminum body and cast tailshaft, and had the big 5 1/4 bearing retainer.
Now you can use the 4 5/8 bearing retainer as a direct bolt on replacement for the larger 5 1/4. It is very close but the bearing retainer should fit and bolt up to the housing and seal everything up. This way you can might no need to machine the bellhousing or bearing retainer to fit? Might double check the input shaft size though, I have a vague recolection that the 18 spline tranny input shaft was larger then the 23 spline? Will have to look this up.
Now with the 833's there were three different tailshafts. There was the long tailshaft and it could have the mounting pads for the shifter either close up by the body, or at the back of the the tailshaft, or could have both. If it was a dual pattern tailshaft generally only one of the mounting locations would be threaded. This longer one was generally used in all B/C/E and truck/van conbos from 65-87.
The other tailshaft was a shorty, used mianly in A/F/M body cars. and has the short tailshaft with the shifter mounting pad located midway on the tailshaft.
This is the tranny I plan on using in Fernando eventually. I hope to be able to adapt it fairly easily.