You can do this by creating your own version of USpinBox in C++. Start by creating a C++ class with base UWidget, and copy over the contents of USpinBox.h and USpinBox.cpp to your respective new files. Then, change a few key areas of the spin box code to use int32 instead of float. Some of these key areas include the following.
A few more similar changes must be made in the .cpp file, but they all come down to changing floats to int32 where needed. Finally, make sure you set your spin box delta to 1.