I can't answer the conversion question. I'm not a believer in them, I bought my propane mowers new from the factory.
Propane didn't make sense financially until we bought a refueling station with a 2000 gallon tank. We got a grant from the DOE and state to pay for the bulk of the it, so the costs were low to the company. We paired it with a CNG refueling station onsite, so we doubled down on the investment.
At 2000 gallons, I'm paying $1.76 a gallon delivered in bulk.
The propane tank exchange or bringing the tanks to the facility was a waste of time and money. If I didn't have the bulk station, I'd probably have a different outlook.
Ask me next year when I have 19 propane mowers in the field and a pair of F-550's drinking from the same pump instead of just the two propane mowers I have now. I'll have better data then.
My season long experiment showed me I will save money with propane in a big way next year. The biggest indication of improvement is the Toro I have now going on 400+ hours with no oil changes save for the original oil change when we brought it into our shop.
One suggestion I have operationally is to add the front weights you'd normally use for the bagger. The tank location is too far back for my liking.