360 downgrading more street

The above sounds good. A good torque converter,can help immensely. A looser than stock converter,doesn't lock up completely at lower rpm's. This helps take the "load" ,off the engine. That can help ,with your decision.
Your downlow says 3:91's. With that cam,roughly a 10",or a 9.5 converter about 3000-3500 in the ballpark. Tuning is everything here. Carb,timing curve should be spot on.Nice find,btw.