Okay, here's exactly how I did it.
-You will need a CW First-Aid figure, and a CW Ironhide figure to do this.
-Super glue or Kraggle/Krazy glue
-Also a dremel with a sanding/grinding bit
-plus a small portion of plastic sheet to cut out Ratchet's crest.
Step 1: remove First Aid's and Ironhide's heads.
Step 2: use the dremel to remove Ironhide's mohawk, and shave down the two cheek guards. I messed up a bit on mine and ended up scraping the nose, so I just ended up taking all the paint off the front surface of the nose. This will make Ironhide's head less like Ironhide.
Step 3: cut out a crest from the white plastic sheeting, curve it slightly, and then super glue it to Ironhide's head. Make sure the crest fits within the boundaries of the head space, test fit on the First Aid body by transforming the figure into all modes and moving it around. This'll make sure that the crest is secure and fits without hindering anything.
Step 4: this is the hard/easy part. The First Aid figure's torso is actually white plastic painted red. So now all you have to do is carefully take the dremel and sand/grind down the parts you don't want in red. I left the waist on mine in red, and removed some red to add detailing. I left the center of the chest in red, since that's actual red plastic, and carefully removed around the window parts.
Step 5: put the gray axe and CW hand/foot onto your new CW Ratchet
Step 6: put First Aid's head on Ironhide's body. give the black axe and CW hand/foot to the new nameless figure I like to call Redneck. (well, I plan on painting him green to make a CW Hoist, but for now he just talks like Dale Gribble).
I left the crest uneven because it was my third attempt and it just looks like some battle damage.