Hehe...my plan was to convert my 22re to an L31 Vortec 350...and then convert that to propane. Costwise it's just a matter of finding all the parts. You can get the stuff on eBay, but I'd rather give my money to someone that will reinvest it in a bus. A 22re will require, among other things, a 22r intake and possibly exhaust. The emissions system may or may not matter depending on what specs your particular engine was built to. I know my 1993 would have had a lot of extra stuff hanging off it in terms of emissions, but none of it would have been functional or mattered.
Probably the best solution would be to use a pre-August '84 22R block (non-lazer block), a 20R head and intake, and '84 or older 22R domed pistons to get to about ~10:1 compression. Obviously there is more to the hybrid than just that, but you'd be using mostly stock/junkyard parts to get a decent little propane motor. You just need to take the cash savings and apply them to things like a good head gasket and ARP fasteners to deal with the 200+ psi compression pressures.