Daniel, on the Pete I'm building with the multi part cab, i built the cab, painted it, then after my interior parts were detailed, I installed them one part at a time. I assume this kit is set up the same way with the interior parts. i had to install the dash and then slide the floor panel into the cab so it would all fit. don't know if this will work for you on this kit, but that's how i did my Pete.
your build is looking great so far, keep at it