Hey Folks,

Removing a 10 bolt from a 69 and replacing it with a 12 bolt rear. Will I need new upper control arms? I've read that the 12 bolt arms are slightly modified while others have said the original 10 bolts arms will work. Any thoughts? Thanks!

The 10 bolt control arms will work. Some of the 12 bolt (and 10 bolt) driver side UCA's have a reinforced doubler attached to the differential end of that arm around the inner hole.
Looks like this...
http://www.chevelles.com/forums/attachment.php?attachmentid=5948&d=1171837311

Excellent! Thanks for the quick response.

I, as well as many others, changed the rear with stock arms with no interference or any other issues and have no problems. Bolt them on, if the driver side uppper is hitting the pumpkin, grind it down a little. There is really no need for the little reinforcement.