how do i link the same gear into 2 slots and a default glamour?

[Iscah]

there's no way to create a glamour plate that dispels glamours.

There actually is a way: use gear that is incompatible with the class it is being applied to.

In this case, to make BLM have the default gear appearance, you'd put SMN or RDM relic gear on the plate. IIRC it has to be from the same group of classes so the glamour will be applied and not just fail.

It's probably simpler to just make a plate that actually uses the gear you want to see. As Hasrat said, you can put gear in the dresser, add it to a plate, then remove the original gear - without affecting the image on the plate. You'll lose any spiritbond and the tag that says who crafted it, though.