Depends on the O.D. of your tires - assuming a 6" sidewall that would be about 32" tall. Works out to around 45 mph.
It is fairly easy to calculate:
3000 rpm(direct drive)/6.50(Rear Gear ratio) = 462 RPM for your rear tires
Rear Tire Circumference(outside) * 462 rpm = Speed in inches/minute
Divide by 63360 to convert inches to miles.
Multiply by 60 to convert minutes to hours.
My 1948 F7 will do about 60-65-ish. My spedometer isn't very reliable so it is just a guess. Once I get past 50-ish, the front end starts to shake and thump and I get the *******. It has the 337 flathead in it. It has a singe speed rear and 20" tires.