Rated rpm is 750 for the 20/1 and 850 for the 22/1.
I like to run mine at around 550-600 rpm.
I'd need to measure the base but its big!
The flywheels are 30" and weigh 310 lbs each.
Standard Listeroids use a #34 injection pump and the 20/1 has a #36 IIRC.
These are GM-90 configuration. (Direct Injection)
This engine is a Listeroid on steroids, it weighs around a ton and the shipping weight on mine w/electric start, radiator, and alternator was a bit over 2400 lbs. I'm 220 lbs and pretty stout but its about all I can do to hand crank this beast as the bore is a bit over 6" with a 8"+ stroke making 500 psi of compression. Even with 600 lbs+ of flywheels it is still tough to hand crank it over compression.
I have many of the factory brochures that I can scan and email if you want to know more. Unfortunately, I don't import these anymore..... But if anyone has a need for parts, I have plenty collecting dust.
Mike