The Yenko Deuce Novas also received them, specifically the round style that has a superceded part # 1565208 with a 1 : .833 ratio for the 4.10 gears.

I have a rounded version with .6481 stamped on it. I pulled it from the same car I pulled a BX code 4.88 rear from.

I've never been able to accurately cross that gear reducer number to anything but it does work accurately with that rearend.

The round reducer with 1:.833 is #6477965

Did the Copo's and Z/28's with 15 inch tires use a reducer with 4:10 gears?

On some cars too with 3:73's

My 1974 z/28 4 speed has that same reducer on it. Its definately the original reducer. Im sure I have 3.73 rear

Here are pics:

Not on Z's. Never seen a 69 Z with one (though they may be out there). Only on first gen Z's with 4.56 and 4.88 axle.

Most I've seen were in BB cars and most were 14" tires. It depended on which trans version they received - there were different speedo drive gears (shown in that chart).
I've seen 2 different adaptors used in 69 - auto vs manual - but there probably were others for the special order 4.56 and 4.88 axles.

My turbo 400 70 Z with 3.73’s has one.
Buddy

My 70 4 speed car has one also. But I have seen many other 70Z's without one.

What I never could understand is the chart I attached a link to. It shows cars with a wide ratio (M20) getting one but cars with a close ratio not getting one. What difference does the trans ratios make??? The internal speedo gears are driven by the output shaft so the gears in front of them make no difference. Not to mention that in 4th, all Muncies were 1:1 anyway. Am I missing something here?

Sorry, clarified that I was only talking 67-69.