Hi,
I always believed that there would be more to it but the engines are identical it is a straight swap requiring no modifications (but I think it would need to be the early 210 E55 lump), but you may have to use the C43 fuel regulating valve as I think it maybe coded.
The chassis modifications if you can call them that, the floor around the differential requires reworking to fit the larger E55 diff unit.
I,ll see if I find the link regarding the C43 being fitted with the E55 lump it has photo's of the engine change, there seems to be a few that have done this and no apparent problems.