The plastic ammo belt should be 90mm tall and go 40mm past the end blocks. Those measurements were taken from an original ANH belt. The canvas belt is 70mm tall.
All of our gear is wonky as hell and it's good!
I think you can sand down the top and bottom edge just a tiny bit more until you're almost where the block begins.
For the left and right side, have a look at screencaps:
They weren't all the same, so don't worry too much about measurements.