Larry,
Don't sell the 4.3L V6 short. It is just a 350 Chevy with two cylinders lopped off. The small block Chevy is one of the longest and most continuously improved engines around. They are very reliable. We have a Chevy S-10 with a 4.3; it is very smooth and torquey through a wide power band and gets 26 MPG highway. It is not unusual to get 200K from one with just routine to indifferent maintenance. Sounds like a good swap to me. There are lots of now elderly MB 123 diesels with tired engines around.