What a brilliant bit of kit that jig is
. Was wondering myself how to drill new leg bolt holes and keep them straight, true and on a 45 degree. Looks like the jig does all that.
From what I have seen all the Williams of this era have a really shitty panel at the back. I had it on a Flash and my Firepower too. Its funny the rest of the cab is ply which is fairly hard wearing and then they use crappy chipboard for the cabinet back and then MDF for the Headbox back which once you get a tiny bit of moisture in it it swells up and is cactus fuctus.
But yeah, great job so far looking forward to how it turns out.