Thank you for this information @john61ct I knew about these adapters, but thought for some reason you could not mix fuels for a butane burner. From what it sounds like, as long as I get a quality adapter and other parts I will have no problem using the propane on my Iwatani 35FW.Not possible, sorry. What for?
If you want to find the propane bottle - to butane appliance adapters, note that USians pro's will rarely have a clue about this stuff, but they're available on eBay through Amazon and elsewhere.
The quality products are from Korea, "G-WORKS" is great quality and service, pretty pricey but includes a pressure adjustment feature, also a variable regulator is useful at the tank.
Terminology for the various fixtures, valve connections : male vs female of course
Butane thin and tall like Iwatani: CP / P220/ DOT2P / CP250 canisters (~ 5/32", 4mm)
Butane wide and squat (usually) standard 7/16 (11mm) UNEF threaded, Lindal Valve, aka "screw style" canisters, EN417 (/ EN521?)
Propane, standard BBQ & other bottles, usually vertical use, vapor valve: Type 1 QCC ACME + POL thread since OPDs were required, used to be POL only
Propane Coleman style 1#: 1"-20
To learn more, google the term + the gas, e.g.
Decent related post here https://adventuresinstoving.blogspot.com/2017/01/the-g-works-adapter-100-propane-for.html