A Saginaw can't even handle a mildy warmed-over 327 for long! You can buy a new Richmond
T-10 (formerly Borg-Warner) 4-speed almost as cheaply as an old Muncie on eBay. If memory serves me right, you'll have to change the clutch disc to a fine-spline, as well as the driveshaft yoke, but a T-10 is almost bulletproof. On the other hand, a Muncie M-20 or M-21 has the regular clutch disc splines and a regular driveshaft yoke. The M-22 had the fine-spline input shaft, too. The M-20 and M-22 had a 2:20 1st gear, whereas the M-21 had a 2:52, I think. The T-10 had the lower 1st gear, too--I think it was a 2:64. The 2:20s were harder to take off on with a high rear-gear ratio (3:08-3:31 etc). Hope this helps.