go the other way. Look up those numbers to see what it is from. They all (the Big 3) contracted out for those units (just like many sub units, components'n parts).
Best bronk source (not sayin urs is) is viperwolf on CB:
Anyone out there that can decode? Are these numbers for real do they match up with a t-case off a '75 bronco? "The numbers on the case are Serial no. tag 1381131 B/M 300777-8 MODEL 20. Case numbers are C18-15-29 , A-2"
classicbroncos.com
He too is a great guy (seems 2B on one of the worse sites tho, only pirate4x4 is worse). Go to the Novac or advanced adapters sites to ID if its a D20 B4 bothering another driver (Viper) tho, do ur work 1st...