I bet the 14 bolt is still a good swap, check the original axle width and compare with info in the 14 bolt sticky thread.
Thanks Grigg! I've read though that thread a few times now to figure out what I need to search for.
The spring perches on the original axle measure a little over 40". The width for the original axle is very similar to a 14 bolt out of a C&C, its just a tad wider.
And it hit me yesterday, I know of a salvage yard with a mid-70s Chevy towtruck that might have one under it. Hopefully the truck is still there, was 2 months ago when I saw it.