A833 overdrive V8 bellhousing?

You can change the front bearing retainer for the smaller size. I have an od trans and big block bellhousing. I got the new bearing retainer online with the 4.8 register for the bellhousing
Ok, pretend I know nothing. Your saying I can change the front bearing retainer from 5.125 to something smaller? this is easy? Once done i can use a more common bellhousing?