I have finally gotten around to taking the digital photos of my propane injection system and have provided a link to them at the bottom of this post.
To refresh what I did was as follows:
I took a motor and tranny from a 83 SD and put it into a 1973 International Travelall (suburban looking). I boosted the turbo to 13.5 lbs, cranked up the fuel via ALDA and intercooled it using a unit from a Ford probe. I also added propane injection, an overdrive unit and started running it on used cooking oil. (SVO)
The addition of the propane was the single BEST improvement as far as power and speed and was probably the simplest to do. Propane is 118 octane and the MB diesel LOVES it!
Before I get into the particulars I must say that if you decide to do this, it is at your own risk and I am not responsible!
How I did mine was starting in the back of the truck I had a compt that used to store the spare tire, like old station wagons had. It is big enough to hold 2 barbeque tanks. Mounted on the tank is an adjustable regulator that I have set at 1-2 lbs. (You must find whats right for you, trial an error). I also have a gauge that reads tank amount (optional) see pic.
From there you run LPG rated hose up to the engine compt. You then must mount a 12V fuel lock solenoid. You want to get that as close to the air cleaner as possible.That way there is no lag when it gets the signal to inject. The hose from the tank goes on one side, an additional piece goes on other side and will go to air cleaner area. (see pic)
To inject into the engine I made up a brass fitting using a male an female hose barb and mounted it to the end of my cone type filter (pic). For a stock air cleaner setup. drill a hole through the "U" shaped piece that connects the air cleaner to the turbo inlet. Theres even a small flat spot on it thats ideal..
As far as activation, You need whats called a HOBBS pressure switch. Use the one that adjustable from 1-10 lbs pressure. On the rear of the intake manifols is a plug. Remove it and screw in the hobbs switch.(see pic) What this does is whatever psi you set it for, it will close contact at that psi,
there by energizing the fuel lock, opening it, and propane goes
in.
To simplify, The fuel lock is grounded to the car. If you give it 12V juice it opens. I wired mine so that 1 switch energizes the system. When that toggle is on and I get to my preset boost amount (at hobbs switch), The lock opens and instant speed. I also added an additional toggle and what this does is power the lock manually. I use this coming off a light with a steep grade. Instead of waiting to build up boost, I hit the switch and propane shoots in instantly. (see pic)
As far as what boost psi I have it set at, I usually run at 5 lbs boost. I just lowered it to 3 lbs boost and now I have power instantly and haven't had to hit the manual button once.
As far as propane usage, I will tell you one experience I had. I drove from Ronkonkoma Long Island NY to Carlisle PA, approx 500 miles roundtrip and through a very mountanous area where the "juice' was on constant and I didn't even use 1 barbeque tank! The extra power is well worth the cost.
When I was setting up my pressure amount at the regulator,I initially had it set at 6 psi. WAY TO MUCH! You know your injecting too much when the engine pings. You only need to bleed it in.I like my 1-2 lbs setting.
AS far as the equiptment needed, My friend got me the fuel lock. Any large propane place should be able to help you out. He uses them on their fleet trucks as everything runs on LPG. Everything else should be easily obtainable.
Regarding the safety aspect, I will not get into it. There are tons of lpg vehicles on the road and I don't see them blowing up.. Also, although my vehicle once resembled a Suburban, I chopped the back, fused in a rear wall from a pickup and created a 4 door pickup. My LPG tanks are now outside the vehicle compt in the bed area
THis is all I can think of for now. I will leave you with this, If you want you Mercedes diesel to be a rocket of the line, do this. You will be amazed!!!!

link:
http://f1.pg.photos.yahoo.com/ph/westkill1/album?.dir=/9adc&.src=ph&store=&prodid=&.done=http%3a//f1.pg.photos.yahoo.com/ph/westkill1/my_photos