I can answer for the 560SEL. I enjoy this engine a great deal, and from what I have read here and in other places, the 5.6l engine seems to be less susceptible to the timing chain rail failures than the 3.8 and 4.2's. The car itself is wonderful, the long wheel base and hydraulic suspension gives a great ride.
I drove a couple of 420's when I was shopping for this car, and found the increase in performance, (when your right foot gets heavy), to be more than a little noticeable in the 5.6l.
I do not see the merit in the OHC design, in any V style engine. While it allows better spacing of the valves in the cylinder head, there appears to be enough room to run this layout with a single cam.
A sleeved aluminum block is not something we are used to seeing in the US, but it is a strong design. The tech's here will attest to this, I am sure, and anyone who has worked with aluminum components knows enough to use anti seize compound and a torque wrench when assembling things. This practice eliminates most of the problems typical to an Aluminum block and heads.
I would like to drive a 5.0 l V-8. I do not see many of them around here, and I believe the lower bore/stroke ratio many let it spin up faster. I refer to the chevrolet 327 vs the 350 engines performance for this hypothesis.
This ends my rambling, for what it is worth.....
1971 Cutlass convt. (sold)
1978 Olds Toronado (sold)
the rest are boring