Larry, the 4.3 Chevy motor is one of the best built by General Motors these days. They have good torque and are very durable. The basic design goes back to 1955 but the refinement in design has made the Chevy v8s and V6s very durable and refined engines.
I,m looking forward to seeing the pictures of the 4.3 in 300TD swap. A swap like this would be very interesting for a 190E or 300E especially if you wanted a manual transmission (which are readily available) and would be an economicial performer.
I say this even though I believe Mercedes Benz engines to be the best but there are alternatives. Mercedes does make motorcycles, snow blowers, or lawn tractors.

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1990 190E 2.6
1996 Grand Voyager 3.3
1985 Mustang GT 5.0 5 SPD
1982 Suzuki GS 750T