Makes sense. The dual mixer setup shouldn't be all that hard to setup, assuming the linkages are synchronized.

Idle should be set when the engine is warm, and the screws should be turned equal turns out from the seated position. The same should be done with the power mixture screw.

How much to adjust it depends on how you are tuning, either with a computer, or on the drag strip. Like I suggested before, If you take your truck to the track with dual mixers, instead of 1... add only 1/8 of a turn on the mixers until you start getting slower.
It may make for a longer day, but power always equals sacrafice.

LPG will never get to the level of energy output as gasoline, but there are other ways to increase the effecieny of it's burn. Since it's high octane, engine compression can reach 15 or 16:1, but thats only for high grade propane. Or you could boost it, which I plan to do sometime in the future.

The cam, intake and headers are a good start. However, too much overlap with the cam can cause issues, because the mixer uses vacuum as the refernce for fuel delivery. Real "Lopey" cams will cause vacuum fluctuations as lower RPMs, making your truck a pain to drive on the street. Franz Hofmann, a long time propane engine builder, reccomends an RV style cam installed straight up, 0 degrees.

Other improvements include building the shortblock for higher compression. Or on the cheaper side, have your cylinder heads shaved .030".