MPG Motor Magnum vs. Hemi

Unless there is something truly wrong with the A518, I don't think you will gain any meaningful mpgs from a rebuild. In steady state operation, the powerloss thru it is not much different than the A500, and only a little more than a GM .
The TC however could be a more likely culprit.
At your Quench, it would be hard to increase the Scr without major cash outlay.pressure however, can be jacked around pretty good with changes in ICA.
IDK anything about LPG, but I think your engine combo is well thought out. I imagine you're a pretty sharp tuner, so you keep after it and i think you will make it the best that it can be.

Your cam tho still has the hydraulic acceleration ramps on it, even tho you're running "solids". That thus makes your cam appear to the engine to be one size smaller @.050. Further more, the lash you are running is stealing another 3*or so of ICA, and a total of 6 degrees less intake and exhaust duration, and so about 6 degrees of overlap.
Go back to post 62 and I'll I add your net numbers as #10, as a best guess as to what your engine is seeing. Compare #10 to #11 the factory 2bbl cam. they are practically dead ringers.