Most 3-speed auxiliary transmissions provide under/direct/over gear ratios, which effectively turns your 4-speed into a 12-speed. There might be a data plate on the Brownie that shows the ratios. If the manufacturer's name and a model number are present, someone here can probably research the ratios. Your 235 can probably pull an OD gear unless the truck is loaded heavily or the OD ratio is too high to stay in the torque band of the engine. I'm about to install a Brownie in my 61 GMC fire truck with a 351 V-6 and a Clark 5-speed with direct drive in 5th. gear. The fire bed is coming off, and I'm going to install the Brownie where the fire pump used to be in the driveline. I'll have 15 forward speeds, and OD in 5th. gear. I'll also install a commercial 5th. wheel and a gooseneck trailer hitch.
Jerry

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