I got my block back from the machine shop with new pistons fitted. I started putting the engine together and found that the prechamber extends further into the combustion chamber than the piston relief accepts. Turns out the pistons are wrong for this engine.

My question is, are there prechambers that I can use that do not protruded into the combustion chamber as far and work with parallel glow plugs etc.?

It would be easier to change prechambers than to change pistons. If I change pistons, I will have to strip the block and return it to the machine shop, and then rescrub the block when they're done to get the honing grit out. Also it could be that the block is already honed to large for the other set of pistons.

Has anyone ever run into this before?

I almost forgot. This is an '81 nonturbo 300D engine number 125XXX.