You might be interested in checking out my web page, which details the conversion of my 1982 Mercedes 300D to a chevy 4.3L V6 with t700R4 transmission. I experienced none of the dramatic problems everyone has implied might happen, and the conversion has been on the road for almost 2 years now with absolutely no problems at all. I've literally not had to change or add anything to this conversion, the only side effect being that the front of the car sits high enough so I wore the tread off the front tires prematurely before I noticed. (I didn't think about alignment until after I replaced the tires!) I made up an exhaust manifold for the drivers side that comes up above the steering box and then down to the crossover pipe - the passenger side worked fine as-is. I used a TBI engine, and installed the fuel pump up on the driver's side fender well, so the pressurized line is less than 2 feet long. (only 13 psi with TBI, so no problem anyway...) The t700R4 transmission works great with the 4.3L V6, and the car gets extremely good mileage and has plenty of power, much more than with the turbo diesel. I am very happy with the conversion, and it drives very well.
The site URL: http://pages.prodigy.net/rwooldridge/mercedes.htm
The total cost of this conversion was under $900.00, and took me about a month of spare time messing around. I got a good deal on the engine I used, and didn't bother to touch it before installing it in the car, a gamble that paid off with no problems afterwards. I'm not sure how much more your car weighs, but suspect it might be in the 300 - 500 lb range. You might consider the 4.3L if you can find one cheap enough! (Mine came out of a Chevy Astrovan.) I'm in my 60's also, and found the conversion an interesting project that paid off handsomely.
Regards, Richard Wooldridge
1982 300D/4.3L Mercedes
1977 XJ6L Jaguar
1977 280Z Datsun 2+2
1985 GMC S15 pickup
1994 Ford Taurus (Wife's car)
1988 Chev Astrovan
1967 Clark Cortez Motorhome!
1986 Kubota DIESEL tractor.... See, I really DO like diesels!