Really good looking job. I think a little cable frey inside the solder would help gripping and keep the cable from pulling straight out.
I like the jig, but how are you keeping the solder from falling through the hole completely? Another plate underneath with a small pin hole to allow the air to escape and solder to fill the cavity?
What type of solder eg: (60/40)? Any special flux?
I have seen a couple other methods shortening the carb end of the cable. Don't trust doing the carb end. If failure occurs, you'l have a bb dropping and being sucked into the intake.
I was thinking of using the brass cable nut/barrel and replacing the bulky Phillips screw with Allen set screw(s). Haven't found a perfect fit without a little filing / drilling. That's easy to do.
Really do like the looks of your end result.