Most important thing is to degrease the snot out of it. I'd use brake cleaner. I would also scuff up the metal and remove the paint with sandpaper before degreasing to give the epoxy more tooth to adhere to. Also, where the metal originally cracked off -- where you can see the cross-section of the metal and all its pores which are now filled with oil and trash -- I would be tempted to take that down some with a file or something, then degrease with about half a can of brake cleaner, then blow off with compressed air, then epoxy.
You don't need months to do this...an afternoon should be sufficient, with 24 hrs after that for it to completely cure.
For more/better adhesion, I would consider using some liquid-type (unfilled) epoxy for the first coat on the bare metal, then immediately follow up with the JB Weld. (You need to get the JB Weld on top of the base coat before it fully hardens -- you should still be able to dig your fingernail into the base coat when you apply the second coat -- for it to bind together chemically without the need for deblushing.) As Guadatoast says, if you allow the first coat to fully harden, you'll need to deblush first before applying subsequent coats -- and in that case, your bonding will be purely mechanical rather than molecular....
Good luck and let us know how it turns out.
ETA: I have to say I really like
atpchas's idea (in post 11 below) of attaching some metal to hold things together and serve as a kind of "scaffolding" for the epoxy to adhere to...wish I had thought of that yesterday...it's a damn good idea. I'd probably drill pilot holes in the saw handle, then attach the additional metal with sheet metal screws. (They're really only there to hold it in place until the epoxy composite hardens.) I might also punch some holes in the metal that you use for this, and fish some fiberglass or carbon-fiber or even polyester fibers (braided dacron fishing line) through it, to act as reinforcing to tie everything together...the more reinforcing you have throughout the whole composite, the better off you'll be. Don't worry if it's rough on the outside -- you can always sand it smooth and paint it after you're done.
