Evening out a Seg

[QVINTVS ARTORIVS CORVINVS]

I am about to retrofit a few of our group's Segs... you know, brass rivets to copper, better hinges, proper Corbridge-B yoke hooks etc.
The one thing I notice on allot of the older ones (and I want to avoid in the future ones) is that the horizontal girdle plates are not even. Invariably there is always 1 side hanging lower... which of course looks like hell.

What is the best method of construction to ensure they are even, every time???

Thanks in advance.

Phillip