The simple fact is that the system is designed to prevent the overdrive from being engaged in reverse.
Mainly because it will destroy internal components such as the blocker ring, the ONE WAY roller clutch, and
likely the planetary set. The reference material that is shown on Deve's site is from the Old Burb Website
and is a good reference. Yes I have rebuilt overdrive transmissions for more years than I care to mention.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine