Nate,

Where did you get your upgraded kit from? I just put my front end together and got mine from Tucker. 1951 3100. The kit you recieved should have the correct bolts in there to replace the current bolts holding the back plate on. Ensure that you look at your instruction manual that came with your kit. I have a digital copy of mine if you need it.
FYI, I have no back plate on mine anymore. Just the spindle, disc, and hub with obvious bearing upgrades. You might be able to see the brakes in one of my pictures.

Chris