I posted on one of your other threads about my LCF. The original rear gear in mine was a 7.20:1 single speed, I purchased a 2 speed pig from another Big Bolt member and it made a big improvement. My drivetrain is similar to your's, 283, SM420 4 speed, 2 speed rear. I have 10R-22.5 tires on the rear, the factory spec'd governed speed for these engines was 4000 RPM, mine will do 65 MPH if I bump it to 4100-4200 RPM. If you do larger diameter drive tires you will be able to hit that speed.
