How much improvement will I see?

I have a 74 Duster with a 360, A500, 4.30 gear. I run 275-60-15 drag radials. Approximately 3500 lb car, maybe more, I will weigh it in the spring. My car is primarily a street car and highway cruiser, but i want to make it as quick as it can be for what it is.
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My best time to date is a 13.36 @ 104.24 with a 2.08 60' time. I got in touch with a torque converter guy from TCS Performance Transmission in Burnaby BC Canada. It's a well respected shop here locally. His recommended converter should stall between 3200 and 3500. My question is, what could I expect for a 60' and ET improvement if I do say get a full 3500 stall from this converter? I know this won't be exact as there are way to many variables, but I'd appreciate opinions by the experienced racers here.

Thanks,
Cley
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What is the current converter? Current 60 ft is soft for the ET/MPH. It will be quicker with a better converter - IF you can hook it up.