If you got the A833 that has the typical gm bolt pattern, It will nearly bolt in. I say "nearly" because some machining will be necessary. The bearing retainer on the A833 is indexed at 5.125 inches. The sm420 is indexed at 4.686 inches. Most people cut down the bearing retainer on a lathe to the smaller 4.686 inches to match the bellhousing. It is possible to bore out the bellhousing to match the transmission.
