La Jolla Independent BMW can give you a list of all the parts you need and supply many of them. Bimmerdoc.com.
Do you have a good 265 that you know works well?
That is the first hurdle. Good ones are getting harder to find. If you pull one from a non-running car, you may have no idea if it really shifts well until you are done.
Conversion from an automatic will require pedals and also a new center console cover, and these latter pieces are getting more rare. I believe coupeking can supply the console piece, but expect to pay.
Not trying to be discouraging, but I would expect conversion cost in the US to exceed 5K dollars. Just being realistic. Conversion from 4 to five speed is a lot simpler, IF you know the 5 speed you have works well and does not need to be rebuilt.
Scott