Martin,
Your website is first class!!! Well done!!!
First hand history from JMC/ACE.....
Going back to '75-'76....
I was growing up in Glendora, CA. I regularly raced at Covina Valley BMX track, as most of the original JMC riders did before Jim sponsored them... There were two brothers that use to race there regularly as well, pretty sure their first names were John and Greg, their last name was Lindsay..... Their dad owned a company that specialized in motorcycle drag racing components. The name of that company was Superbyke....
Bakton Ent. may have manufactured the stems for Mr. Lindsay (Superbyke) as they likely did manufacturing for his motorcycle products as well.The design and testing was Superbyke.... I was there,, the first time one showed up at the track (Covina). The Lindsay brothers had prototypes on their bikes and their dad had one in his hand..... How could i forget that!! This stem was totally different than anything we had ever seen before!!
All of the Tuf-Necks we see today are different from the originals...
The 1st version was simple it had the quill shaft pressed into the aluminum block and relied only on the wedge bolt to keep everything together. This wasn't working so well. After a bit of riding the stems would loosen and begin to creak.
The first upgrade...
Drill a hole in the back of the aluminum block that would protrude into the shaft and pin the two together in this manner. This was an attempt to lock the two pieces together and not realy on the wedge bolt alone to keep things in place.... This was an improvement but not the solution. The wedge bolt would still continue to loosen and the creaking would eventually appear as well.
The next upgrade is what you see today...
The shaft is pressed in and a hollow bolt secures the block and shaft together as one. The wedge bolt uses the top surface of the hollow shaft bolt to torque against instead of the aluminum block.... Problem solved!!! Thanks to the hollow shaft bolt, no more loosening of the wedge bolt and no more creaking.....
These upgrades were performed in a matter of a couple months...
If my memory serves me correctly, I remember people with the first two versions being able to trade in those for the final version. To find one of the first two versions is next to, well you get the idea....
Below is a scan of the original product, (1st version)

Original Superbyke decal.... Drag bike roots!!!