I once looked into doing exactly that on a 350. It takes very special, hard to find injectors. There are problems with speed of vaporization. Do a search under "car and driver" (magazine) and "propane". They had an article on conversions on Crown Vic's that were f.i. There's an issue with vapor purge on first startup. The C.V. conv. used the dome light switch to trigger the purge cycle.

I like propane for the 130 octane and very clean burn. I've torn down traditional "mixer" propane conversion engines at 250k miles, and the combustion chambers and piston tops and ring lands were as clean as a motor with a blown head gasket - in other words, shiny clean like new castings.

Mixer is just a propane carb. Works fine, but not technically elegant, and not what I wanted for a turbo 350 in the old FJ55...