So a "short box fender side" would be a flare side?
Lets see some pictures as we love pictures.
The 3 speed is that on the tree?
If so dont trash the parts in the column as they are hard to come by and some are looking for parts.
I dont have anything with the NP435 or and of the granny first gear transmissions but got to ask what will the truck be used for that you want to change the rear gear?
Also unless you have an over drive unit to use with the 3.73 / 4.11 gear I would not go much lower than 3.50's if I was to check it at all.
I have a 300 six with the NP435 and 2.75 rear gear and between the motor & rear gear it will never be a stop light killer but gets the job done. BTW I do have a over drive unit and still dont think I would go lower than 3.50 gear set but what I use the truck for the 2.75 work just fine.
Dave ----