So my car has a GM 12 bolt rear end from a car. Its definitely not a truck rear end. The previous owner installed mini ladder bars to the sub frame connector, which I assume was done because there was no torque arm. Does anyone know of a company that makes a bracket or anything so I can add a torque arm to the diff and go back to using lca instead of ladder bars?

 

Nothing off the shelf. Possible you could have a good fabricator mimic a mount like the 8.8 swaps use. Could do a DSE quadralink as well I believe. Wouldn't use a torque arm, but would probably work better than ladder bars on a street car. Other option may be buy a bare 12 bolt swap housing and swap your parts over.
None of the options are gonna be cheep

 

https://www.thirdgen.org/forums/memb...oming-aka.html start around post 849.

Also, see what GM did to fit a torque arm to the Buick GNX, which got a torque arm using a cast rear cover. (vs the Grand National and Turbo T which had hotchkis style 4 trailing arms.)