You have the right idea with shaving the ball on the head. I'd suggest using some 1000 grit sand paper(automotive type is fine) or using a nail file and then smoothing off with the sand paper. Go slowly and test fit it often, as you can easily sand more and don't want to take off too much. Good luck and have fun customizing
Just a little more info on my problem if that alters the advice at all. My main dillema is the additional plastic on soundwave's head and or the length of the ball peg on bumblebee. I'm stuck between either shaving off plastic around the peg or shaving off plastic on the head. The peg is not static and sits on its own joint that connects it to the body, which I'm afraid will weaken and break if I shave off plastic there. The plastic on the head comes off of the head's ball socket, which I'm afraid I will ruin by shaving around it, making the head useless unless I glue it or something. One thing I noticed between the two figures is that soundwave's head peg is longer than bee's so at one point I thought of cutting them off and gluing them back to the new body. My thinking now is that it would be a drastic step, and I risk irreperably ruining both figures. This idea is actually based off of one I saw on youtube by Gabstaify http://www.youtube.com/watch?v=KeZo29okh0c
only I'm trying to make sure this version can still transform. Can anyone tell what he did to make the head fit? It looks to me that the space between the head torso and peg is larger than it would be unaltered on the same mold but I can't really tell.
Anyway I was just providing some more info on my dillema for anyone who wants to take a crack at it. Thanks for any and all advice.