Got my new converter

I am getting ready to pull the trigger on a convertor for my slant in the 66 valiant. any tips or suggestions? 225 with .120 milled off the block, ported head with oversized valves, Erson cam ( cant remember the spec's right now ( nothing crazy about 460 lift? ), Aussie intake & Clifford headers. Mostly a cruiser, might get a torque storm blower down the road. I put an aftermarket 1800-2000 stall that was behind my 318 in it and its way to tight, almost stalls the engine when its put in gear.