When I built The Frenchtown Family Truckster drag car I did some computer modeling using a 4000 stall converter and either 2.47 or 4.56 gears in the rear end. The computer said 11.60s with the 2.47 gears and 10.90s with the 4.56 gears in. I never put the 4.56 gears in (that was going to be for the NHRA 10.90 heads-up class, which I haven't pursued yet) but it did run a 11.61 w/ the 2.47s.
If your current converter is stock - assuming around 1200 RPM - you'll see a sizeable reduction with both the gear change and the stall speed change. I wouldn't bet the farm that it will be a full second but it wouldn't shock me if it was.
One of the big "ifs" is whether you can avoid excessive wheelspin, which may entail taking a look at better tires and rear suspension mods. One performance upgrade often necessitates changes to other aspects of the vehicle.
