First off, your existing set-up has the front motor mounts is located besides the harmonic balancer and the rear mounts is at each side of the bellhousing. If you change the transmission to a 350, you'll have to buy a kit from Danchuk that bolts on to the 350 transmission at the stock location as discribed above. If however, you decide to buy and install a transmission cross member which is located at the rear of the transmission, it's recommended that you install side motor mounts instead of using the stock front mounts.
If you want to keep it stock looking, then look for and install a '55-57 cast iron powerglide. But if it was me, I'd go with the bellowhousing conversion side mounts. Good luck and have fun with your truck.
