My first roadster had an olds in it they were fast in their day.. the 394 is a direct bolt in with only the corect pilot ring for the torque converter required. cheaper horspower if you can fing a good one. bigger valves etc. 57 J -2 multi carb setup looks great. most likley you have the 4 speed hydromatic they were the auto trans for racing in the 50's and 60"s B & M were famous for their racing trans's. they only drawback was the siamesed exhaust ports some racers added a divider plate ( welded into the head) to have individual tunned length headers.