Your best bet is to contact one of the known high stall converter builders. Give them all the information on the engine specs., the rear axle ratio, rear tire size and what your main use of the car will be. With that information, they'll be able to tell you what converter is best for your application. It could be that the converter you've got now is the best one for the car. It looks to me like the car was purpose built for racing and will need to be de-tuned for street use.
Any converter in the 8" diameter was never intended for street use.
