Can you fit...
 

M117 cylinder heads from a 1990 5.0 engine onto a 1990 M116 4.2 engine? I ask 'cos the heads need a refurb on my 420SEL and rather than take it off the road for a while, I can refurb the heads on my spare 5.0 motor at my leisure and then pop them on...

If it is possible, is there any advantage or disadvantage to doing this?

Cheers, Martin

I was wondering about that with my 300 k kms 1990 560 SEL - wanted to know if I could pop on the heads from my 116 k kms 1991 500 SE.
The valves on the 560 were getting a bit noisy - hence the question.
But I ended up selling it recently, afterall.

But I'm still keen to find out if you could do yours.

Unsure, but knowing MB I would place my bets on "no". It's a different motor generation, which usually involves a complete redesign.