I don't know how original you're wanting to stay, but.... Have you thought about a modern rearend? The 04-12 Chevy Colorado Z85 and Z71 trucks had a rear that was 60-62" wms. They have a 6x5.5 bolt pattern, but metric lugs. The rim centers are larger, so aftermarket wheels would be required. You can get ratios from 4.10, 3.73, and 3.42. A quick search on car-part.com show they can be had for cheap all over the country.
