383 build no power

Ran into this with several builds that were brought to the shop, You need a 3000 and up converter . The one you are using is for a truck and used for towing. We put factory spares on a car an 410 gears with that same converter you couldn't spin the tires with guys picking up on the rear of the car. We installed a Factory 340 converter behind a Big block It stalled a 3300 usually 2800-2900 behind a small block. You could not hook the car up on the street with 276x60 15's. It would turn the tires through second gear. Also set timing at 15 before initial and 35 before total by shorting the advance.