Clifford has some nice stuff.

We ran my dads old 300 six off of propane and built the engine up with 12.5:1 pistons, put on a header/free flowing exhaust, and amped the ignition.

With the slow burning-high octane propane and the long stroke of the 300 six that truck had great pulling power and got good mileage out of the propane.

Abe