Mystery Boxes in 72 911 RSR
 

Here's my first real post here. I am Rick and I am involved with an early RSR clone build and I have come across some items that have been hard to find.
Note that I would like to know what these are and how to fabricate something that looks identical but doesn't have to function.
So far I have heard that this is part of the engine rev limiting system and connected to the cable drive on the engine.
Any help with explanation or dimensions would be great. \
http://forums.pelicanparts.com/uploa...1714048692.jpg
http://forums.pelicanparts.com/uploa...1714048692.jpg
http://forums.pelicanparts.com/uploa...1714048692.jpg
http://forums.pelicanparts.com/uploa...1714048692.jpg

10k tachs were cable driven on some of the cars

One discussion about these boxes is that they are part of a rev limiter system as mechanical tacks have no provisions. U can see VDO on one of the boxes.

I have absolutely no experience with these shown, but to me it looks like a Classic Tach Generator, from my aircraft experience. Standard housing and connectors. These look close to the “AC” brand components I used to assemble. The tach generators were about 18” away, aft of the firewall in the nacelles. In the case of the aircraft (twin engine) I am thinking about, the engine was a ways from the tach. A cable would need to run 12 feet and that induces a rotational whip which would make the tachometer needles be almost useless. The middle component looks to be a gear reduction unit, probably about to adjust a ratio. The third unused connection would change the input rotation direction.