Thanks for your help pointing me in this direction.
Ps>Print>Check the Center box
Set up custom paper size/s with 0 in all of the 4 margins.
You can enter a very small margin (.03 or .05) on 1 or 2 sides if necessary if there seems to be a slight paper shift, or just to compensate for an individual printer's idiosyncrasy. Just to nudge it.
Save as a preset.
I made separate presets for all my common paper sizes and a Vertical & Horizontal orientation version for each.
Ive tested it with some small size prints (6x4, 5x7, 8.5x11) and they all appear to be printing properly centred (within a very small tolerance).