Keep in mind that the questions you are asking (head work, turbo, tranny swap) are not done very often on BMWs because this is advanced, difficult and usually expensive work, so there are just not a lot of people that have BMW specific knowledge.
I could give you a general answer on head work or transmission swaps, because I have done this on GM V6 engines, but would that be useful to you? Probably not, because I don't know the details on BMWs, and the DEVIL is in the details.
With that said, I am pretty sure that you are going to need more than just a manaul transmission for the swap. You need to keep in mind that the transmission connects to the ECU and the ECU is more than likely programmed for an automatic transmission profile. So you may need to figure out how to fool the ECU, or adapt the connector wiring, etc. The DEVIL is in the details.
Head porting and polishing is fairly generic. There are a number of books available at the big book stores that discuss P&P as part of an engine build up. Even if it is a build up for a Chevy 350 small block, the P&P techniques are the same.
If you are serious about doing upgrades like this, you need to visit a BMW forum where the racing guys visit such as
http://www.dtmpower.net . But I warn you - BMW Board is really a friendly forum, and we are pretty good about not flaming, ridiculing posts, etc. The racing forums can be tough on newbies. If you post your questions in the style you have done here, you may get some less than helpful advice. You need to research your problems and questions before posting on those forums. Asking "I think I have a vacuum leak, how do I find it" will probably get flamed or go unanswered.