That stop-pin in the speedo at 10 or 20 mph is not unusual in mechanical speedos that go to 200 mph. In 41 yrs of driving, its only caused us a problem a few times, once during a time-and-distance rally where a 2 mile long section ran through two school zones and we were required to proceed at 10 mph.... Judy had to drive slowly until the needle flickered, then slow again. And due to public perversity, there's a section of narrow road in the hills near Saratoga, CA that has a posted speed limit of 9 mph! Both of these were encountered pre-GPS.
The Pantera SI uses a tiny electronic generator on the angle drive, eliminating the cable. The $300 Autometer 5" OD 0-200 mph white-face speedo that some use in their Panteras eliminates both the cable and the angle drive and runs directly off the ZF extension shaft tang. You have to assemble the $100 electronic speed generator from a second source (details in the archives). It wasn't worth $400+ to me to eliminate these parts.