I thought most of the 4106's were 4.125:1. Is there a way to find out without taking the rear end apart?Todd -
Unless it's been swapped out for something else, yes, 4106s came with a 4.125.
IIRC, there's a number stamped on the differential input U-joint yoke, under the U-joint. Dividing either the first or last number into the remaining numbers gives you the ratio.
You've got a 4106? Rather surprised it's got a 6V71 in it. Have you checked the cam pulley on the radiator end of the engine? The engine size is molded into the pulley center.
Be aware that if you're going to install a 730 into a 4106, you're going to have to cut open the bulkhead for the transmission to fit.
FWIW & HTH. . .