I applaud your tenacity, and your ingenuity in cobbling up a toe/heel shifter.
I doubt any existing toe/heel lever from another bike is going to do the trick. (What other bike? I was thinking a T3....)
I'd say think through your needs/desires for a shifter as carefully as you can and then go see a welder, preferably one who has experience with bikes. (Maybe a Harley custom shop could point you to one.) Take a sketch, drawn full size, and ask for his input. Work with the welder to get what you want, and then pay as much as is needed. This will pretty clearly be a big part of your happiness going forward, so I think paying up for the best you can get is a good investment now.
Good luck.
Moto