The engine you would want is the 117.968 code 822. That's the high compression version with the special exhaust and cams.

I would recommend against such a conversion though, unless you have a whole 560 SEL to 'steal' parts from, as there is more to it that just the engine.

Carat by Duchatelet are slightly more special cars... they generally have nicer interiors, and sometimes special bodykits and wheels.

If you wanted more power, fix your current engine, and if you're lucky, turbo technics might still have a twin turbo kit available for your engine. That should give you at least the same power as a 560, if not more. The last I heard, there were only a couple of the kits left, and they were just over £1k.