Thanks for the advice. Unfortunately, it wouldn't be worth pulling the heads on this car. The whole thing is very worn out in every way. Pulling the head means replacing a lot of parts, and I'm not sure how bad is the lower end. Stem seals might last for a year or so, but maybe not.
I've got to focus on the 220S and 300D.
I'll try to find a good home for the 4.5 though. Either a motivated DIY'er or a Mercedes dismantler that'll make use of it and not crush it.