This site will let you figure it out.
http://www.drivetraindirect.com/t_gear_calculator.htm

Just enter your tire outside diameter (measure with a tape measure), and your rear axle ratio. Then decide what is a safe max continuous engine rpm for driving, I would recommend keeping it at about 2,500 or less for your engine. 3,000 is defiantly too fast if you want your engine to last a while.
Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-