David:
In a post by Al Lydon (for his 1996 SL320), he wrote about using a hex-shafted TORX bit, too.... but he had to GRIND down the shoulders of the hex-shaft near the head of the TORX bit in order to make it fit properly.
So, you may want to try grinding the shaft of your 3 1/2" TORX bit as well.
The tool I made came from a slim-shafted screwdriver, and was noticeably thinner in diameter than a hex-shafted bit.
Here are my "Before" and "After" pics of the steering wheels for my 1995 SL500.
I really love the look and feel of the leather & burl wood steering wheel.
The new steering wheel also has custom 'grooves' cut into the back side of the wheel that your fingers wrap around.... a super-comfortable grip, especially for long rides.
Subsequently to my taking these pictures, I added a black-&-silver Mercedes-Benz logo medallion that covers the 3-Pointed Star in the center of the steering wheel.... looks really good.
I should post a pic of this medallion on the steering wheel, in the next day or so, for your consideration, .
Good luck on your project.
God Bless, Arctic