Originally Posted by Hollow65
Auto trans and stock mounts.
Using the stock rear engine mounts I doubt you will find any big tube, large collector, off the shelf, passenger car headers that will work.

Have you considered fenderwell headers? These are 1-3/4" tube x 3" collectors and have some dimensions listed... http://www.speedwaymotors.com/Dougs-Headers-D355-R-1955-57-S-B-Chevy-Fenderwell-Headers-Plain,25015.html