Hi,
A 55 lump fitted in a C43 is a direct swap and as the C43/E55 ECU has the same Pt. No. allegedly, it will run perfectly, and I have read other forums where this combination actually improves the performance over the CLK55/E55, but when the 43 ECU is chipped to reflect the 55 engine fitted it actually reduces the peak torque/power quite noticably though I have never seen any rolling road graphs/printouts to prove this.
The 55 gearbox I don,t believe is a straight swap, as they were mainly tiptronic though this can be retro fitted, It would be a nightmare to source the parts, wiring looms ECU etc.
The 55 engine on E-bay I think is a bit expensive if its the one I enquired about, he wants £2495, and he could,nt tell me for sure how many miles it had done, and at that price I would want to know and have all the ancillaries to.
I offered him £1800 cash (outside of e-bay) and I would pick it up, he did,nt reply, so I took as a no.
I was a bit gutted actually I was away on buisness last week and there was a CAT C w210 E55, 1998 on an S plate, 12 months MOT, still very much road worthy, that only went for £2450, and at that price for a complete car I think the guy is dreaming to expect that sort of price for just an engine and not even sure of its mileage.