D-Jet on a six is very rare in the US, all the examples I know of are
grey market, not officially imported. Carbs up to K-Jet, in 1976.
D-jet is NOT more efficient, it's actually very difficult to get it set
up to give correct CO at idle and acceptably rich mixture at high
rpm/light load -- there is a reason MB switched to K-Jet (mainly
emissions). D-Jet would have fried a catalytic converter in no time!
For those brave enough, K-jet equipped M110s aren't all that uncommon,
and the only major change needed is to swap the fuel pump, beef up the
fuel lines to handle 90 psi, and wire in the cold start system --
everything else is on the engine.
Peter
