Would it be worth it?

[Wanderer]

There's several auctions going in my area which have old CNG shuttle vans for sale.  (12 Passenger types)

The interior conditions are good and so is the exterior. Just the engine is a CNG.

Would it be worth yanking out the CNG engine and replacing it with a gas/diesel engine instead? 

Or would that be impractical?  there's 4 tanks per bus, two have been pulled along with the fuel lines...

 

[DannyB1954]

I don't think they make different engines for CNG or propane. Depending on the year and smog laws where you are it could be easy or very difficult to convert that engine back to gasoline.
Also depending on your location it could be easy or very difficult to get a commercial vehicle insured or reclassified as an RV.

 

[highdesertranger]

x2 on what Danny said. highdesertranger

 

[Presteaux!]

There are places that convert gas/diesel engines to CNG. So I would imagine the reverse would work also.