What 1/4 mile time should i expect from my 454 with 391 gears?

The vehicle is a 1946 ford pickup.
Motor is a chevy 454 with a mild cam and full exhaust, with a turbo 400 3 speed auto trans.

It doesn't feel super fast, but what 1/4 mile time can i expect?

The 454 in a lighter vechicle can do mid 12-13s or better, what your truck does is a different issue.

You put a Chev in a Ford? Sacrilege…
Your quarter time is a function of power, weight and traction…

Any idea of HP? Mid 13's possibly with a mostly stock early non-smog motor depending on wheel spin off line… Need more info on vehicle weight, tire size, rpm's at the end of 1/4 mile, rpm range of max power/torque, HP/torque figures, etc. Big blocks need to breathe so anything you can do to improve that will really help… Correct size /style headers, heads/mods, intake, proper carb, higher stall torque converter to get in power band quicker, etc.

Various sites have online calculators you can plug in some variables to see how well it will do with some fudge factors such as tire slip, axle loading, suspension setup, etc. Only way to tell is make some runs.