Larry, I have had the same experience you are having.The slanted tip prechambers are for the 1st version engine and the round tipped prechambers are for the later uprated version. It looks like your supplier did not send you the right pistons for your engine number. I am assuming that your pistons have the Star shaped combustion recess instead of the saucer shape with the recess for the slanted tip precombustion chamber.
I think your best fix is going to be to change the precombustion chambers although this will set you back another $ 200.00 on the rebuild you are doing.

Good Luck

MBJOE

Shadetree Mercedes Mechanic

83 300TD
81 240D
75 300D