I have a 65 sport fury conv with some mild mods ( bored out 73 400 hp block with 9o6 heads and purple cam) just had trans rebuilt. i have a 24 to 2800 stall cnvtr. I have the original 8 3/4 rear with 2:93:1 ratio in a 741 case . do they make posi or sure grip for the 741 case I dont drag race i only would like this heavy car to MOVE! I know I can swap out for a 742 or 489 id like to keep cost down by using my parts id be happy to even just change the ratio. Any ideas would be great.

 

Any sure grip will work on all three of the cases - 741 - 742 -489, however at times it harder to find only the sure-grip at a reasonable price now days. I have found it less expensive to buy the entire chunk/sure grip. If you do this beware of size of the yoke so you dont need to buy/modify a new driveline -

Craigslist

 

Any drive shaft shop will have a conversion U joint if you need to adapt large to Small U-joint. I would look for a complete 3.23 sure grip diff...

 

there are copanies out there that will sell you center sections for your 8 3/4 but you can go to a swap meet and pick one up for about the same cost and drop it in with uot having to mess with the insides