If this helps anybody, here's the "master" list of speedo pinions still
availble for 66-75 Mopars (fit all transmissions versions):
# Teeth P/N Color
*24 3410024 WHITE
*25 3410025 BLUE
26 2538926 RED
27 52068149 WHITE
28 52068150 BLUE
29 52068151 BLACK
30 52068152 YELLOW
31 52068153 GREEN
32 52068154 BLACK
33 52068155 YELLOW
34 52068156 GREEN
35 52068157 ORANGE
36 52068158 RED
37 52068159 WHITE
38 52068060 BLUE
39 52068061 GREEN
40 52068062 ORANGE
41 2538941 RED
42 2538942 WHITE
43 2538943 BLUE
45 2538945 (Discod -ref.only)
* These pinions require a special adapter, now discod (2892994.) Allothers
use 2538608. Don't forget new seals - pkg. 4883434AA