Since your engines run the same RPM, it should be pretty easy to rig something up and get it flowing correctly. The correct amount of LPG used to fumigate the intake on a diesel will make the engines run more efficiently. The propane will ring out some extra power out of the fuel oil. Here is some good reading on the topic..
LPG (Propane) Fumigation for Diesel Engines
LPG (Propane) Fumigation for Diesel Engines