I was thinking that since I have the reel removed I could sit the mower on a level surface (my shed floor) and use a height gauge at either end of the bottom blade to set the height before tightening the roller bearing nuts. Will that work?
G'day
CarinaBobI suspect you very well know the theory here.

Yes, the datum point is a level bottom blade....
[this is not adjustable]
The rear roller is then adjusted to parallel the bottom blade.
Your method is certainly one valid approach.
The last thing to adjust is the front roller - for parallelism.
This may require physical twisting of the front roller bracket ...
cheers-------------------------
Jack