To add another note to this thread....
As you all know, one of my cars in the stable is a '93 300E 2.8. I absolutely love it, and when I went looking for a 124 chassis car, I remembered the wonderfully smooth 104 motor in the limited run 300E 2.8. I have driven many an E320 and many a 300E with the 103 motor but when the final decision came, the 104 won hands down. Extremely smooth and certainly powerful. We just returned from a trip to Atlanta with the 2.8 and it ran like a top the entire way there and back. Right now, it's at 64,000 miles and no trouble to report. There's some slight seepage at the rear corner of the head, but that's normal, and everything else is cherry. In my opinion, the 2.8 motor was the best match for the 124 chassis (save the 500E).
Precision Motorcars, Cincinnati, Ohio
'67 250SE Cabriolet
'93 300E 2.8
'74 Jensen Interceptor Mk.III
'81 DeLorean DMC12
'84 BMW 745i Turbo