318 combo

Given that you're looking at a 8:1 compression on LPG, I would be surprised if a cam manufacturer like wade or crow don't recommend a cam with more duration (and therefore possibility of more lift) cut on a 112 or even possibly 114 LSA. maybe even with a few degrees installed advance to boot.

I'm no expert on camshafts, but I would be trying to get that IVC happening early early early!!