The pre chambers do need to be the right type for the pistons. The newer pistons are nearly flat top and use a pre chamber that has a rounded end on it. Thes will take either the non turbo 616 pre chambers or if you machine the head to except the turbo pre chambers then they will work fine. It is most likely with your older engine that you have pre chambers with the slanted bottom. If so you are stuck with them. Just ream them out and be happy. The newer pistons do not fit the older block as the bore is slightly differant. I would also say because you are not going for broke on hp this would be more reason to just ream the existing pre chambers. Ultimately I want about 200hp out of mine so built the head to allow that. Yes yes the pistons will melt and all will fail, but in truth I do not beleive that. I use max power very rarely but sometimes more is nice. There is a 240 out there with a 616 with dyno proven 245 hp. stock internals. So can not really say these are weak engines.

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1977 240D turbo