Here's a good way to use the RiD prime sword. All you really have to do is cut the handle and shave down the end of the sword. I'll post a picture of just the sword later but here's one photo of the finished (or close to finished) product. Hope you guys like it!
I did this a while back--I prefer this look to the others I've seen so far. You can do the same with his gun if you disassemble it: http://www.tfw2005.com/boards/radicons-customs/602706-prid-optimus-prime-minor-mod-repaint.html
Here's a pic of the sword. Sorry about the quality I'm using my IPod touch to upload and take my pictures.
And here's how it attaches to the arm. Just unscrew the two screws in the arm and when the handle is cut and drilled the hole on the other side of the port, put it through the first screw bar and screw the red arm piece back on.