360 converter
8-1/4" axles are alot stronger than alot of people give them credit for. In that early A-body it should live a long time.
I had one in a truck I raced for a few yrs. Ran it over 500 times and it ran 14.40's and weighed 3800 with me in it. Raced it on the weekends and used it as a truck during the week and sold it at 90,000 miles and the rearend was still going strong. The guy I sold it to pulled a stump grinder all over the place and finally after it passed 130,000 miles (hard ones too) the rearend went out. I wouldn't worry about it unless your planning over 400 hp and sticky tires and racing it.