Should be a NP-a833 not a NP-435
I just finished rebuilding my a833 and have been getting close to putting it behind my 292, but keep running into hurdles. My shifter had been welded internally and I couldn't get it into OD. The bell was cracked and 2 of the holes the theads were stripped. Haven't pulled the truck apart yet. I found another bell and shifter, fortunately.
It sounds like you've done your homework, hopefully you're starting with a better setup than what I bought.
To answer your question, no I don't think it would be worth trying to modify your existing bell to work with this tranny. The mating surface would have to be built up and machined down where you need the bolt holes. Some of the scatter shields may be a possibility though...
