Check out this custom shift “knob”

I really hate to rain on such a great looking idea. but,
Before I would go thru all that trouble, I would put the shifter in third, and mock it up to see where my knuckles will be, when I ram that gear home.
And I would also try reverse.
If you can't find enough room, then you will have to bend the stick. But then you better put it in first and fourth to see how awkward that might be.
You might have to shorten the stick. But if you have a bench seat ...................
Then there's the fatigue issue.
After a day of just tooling around, nothing is easier on the wrist and forearm, than a plain ol' ball. You can shift those from the top, the bottom, and/or the side. You can full-grip it, half-palm it, or knuckle-ball it. You can two finger it, or palmslap it. There's just so many ways to shift a ball.
I really hope it works out well for you , cuz it looks killer.