Sounds like what you have is a standard 635CSi with Motorsport bits.

I am not aware that you can simply fit a 24v head (which was meant for
the M88/3 3453cc engine) to the M30 block (3430cc).....

Still, your call....

--- In bmwe24club@..., "dave ell" <dave.ell@b...> wrote:
> i think things are getting a bit confused.
> my shark is an M 635 but at the moment has the original 12v m tech
> engine still fitted.
> this means the battery tray etc is m tech set up.the only reason for
> fitting the 24v version was to gain more hp & acceleration.
> this also means i can still use the car whilst rebuilding the
> original lump,however if the changover involves a lot of modding
then
> this isn't really an option.
> regards,
> dave.ell.