1934 Model BB speedometer gear - will a '35 fit?

[More Dust than Rust]

Took a the speedometer gear out of a junk chassis my brother had - it's a later year big truck, we think 1935. Many of the parts look to be the same as my '34 and was optimistic this would fit.

The speedo gear seemed to go in properly but the cap would not thread in correctly. With the help of a bigger wrench, I was able to strip the threads off it pretty good (luckily I have the one from his chassis). The cap initially came off my truck real hard so I am not sure if it the difficulty in replacing it is due to it being a bit bugged up to begin with or if the speedo gear is cocking it slightly - or something else. The worm gear on the drive shaft looks to have larger flights but the gear did spin somewhat without the cap in place when I jacked up one rear wheel and turned it. I couldn't tell if it was properly aligned though.

I am not concerned if the 21 tooth gear is the proper ratio for 700-20 tires, just want to get the needle on the speedometer to work. I can't go fast enough to worry about my speed anyway.

The gear has 51-71-D-21 on the face.