I spent about a million years applying varnish to the handle, and despite many distractions, I finished and rubbed it out today:
Since I was on a roll, I decided to finish the job today, too. First, I cut off the old handle, filed out the notch where the back fits into the handle, and drilled the holes:
Finally, I filed off the rough edges, put the blade into the saw, and inserted the mounting hardware.
I haven’t had time to really test it out yet, but it seems to feel okay in the hand.