If you are really interested in propane do a search in the forums at www.ford-diesel.com , there is a lot of info about how this increases torque and hp there. On larger V8 engines (7.3L) there doesn't seem to be any ill side effects, these engines were built for much higher torque and hp than a little mb engine, also they are much newer.

__________________
1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k