D6 9u top roller height

On my old 9u I have people keep telling me the top rollers need to be the same height. On my machine the back one is higher than the front one. The back one is on top of a plate that's probably 1.5" tall. It looks like a factory one. The front one don't have one so it sits lower. Is that the way it's supposed to be? Serial number 23051.

That's how it should be, 9U1-9U28327 had a higher mounting pad in the rear. 9U28328-up had mounting pads that made the roller position level. It was a good thing to have on the 8U models as it would help keep a slack track from rubbing on the final drive case. Wasn't so critical on the 9U's.
The lift got even higher if you change to life time carrier rollers mounted in the early type stands.

My D6-9u serial #21332 has level track. Should I install 'platform shoes' ...hhaha