first question, where are you?? this impacts alot.
second, unless you dont have anything else dont run a 20R exhaust, run a 22R stock manifold. it flows better and will bolt right up.
propane will run great with a high compression ratio. but you want about a 325 cfm intake so what are you using for a "carb" with the propane setup??
I'm in california, the truck will be strictly off-road. So I have no emissions limitations. I've got the stock 20r intake bolted up..LCE adapter for the 22r carb base as per the GotPropane setup. I do have what I think is a stock 22r exhaust manifold.. but it has an 02 sensor on it...?