a question about bk

BK's are decent ESCs. They were the standard about 2-3 years ago. From what I know they can't handle any motors with more than 2 poles very well, and sometimes they can be a pain to program (and have a lack of programming options). They were some of the best of their time though.
Oh, and in case you didn't know, the 99 means it can handle 99 amps, and the 20 means 20 nimh cells. Make sure to use an LVC if you are using LiPo though.

It looks like a great truck though, congrats!