How Gearing Effects HP from 1-3rd in 727's

I recently made a mod that increased my hp at 2600 RPM by 84 hp in 3rd gear on the Dyno. I was wondering how much of an hp increase that would be in 1st and 2nd individually.

I have a 1970 Duster, 3:55 gearing with 15" rims in back I can get the tire size if you need it, but the speedometer reads 100% perfectly accurate with the set up I have now: the 3:55 gears and the large rear tires I have.

Engine is a 1975 360.

Thanks,
Bob