Back in the mid 70s I worked for a company in Tampa Florida (Dancy company) that did all things propane. it was the height of the "gas shortage" so we had all the business we could handle. the company did the conversions for all the local phone company trucks, and they survived well over 200,000 miles on straight propane. pull the pan on one of those and it was clean as the day it was built.
the dual fuel conversions were mostly IMPCO and were a simple ring that went between the air filter and carb somewhat like the early nitros kits. I doubt I would even recognize the propane technology today, but the principal would be the same.

Russ