Inline 6's

I have an old inline 6 that runs on propane, it's quite gutless so I was wonderin if there were any easy and affordable ways to give it more power?

Remove tha factory intake and exhaust (you DO NOT want a heated intake with LP), and install an exhaust header (or late model downpipes off an EFI engine) and a bette intake. Neither are particularly expensive, and both will help a lot.

If I put headers or downpipes on there, will it cause a great amount of heat?

What size engine? 300 or 240?