The existing glass I have has a metal band all around it.
I assume your truck is a pre-51 with the one piece door glasses?
If so and by metal band you mean like
this? The frameless examples you've seen without are more likely to be aftermarket kits with tempered glass.
The original lower sashes are designed to work with the metal frame and are joined with small double ended bolts,the felts are also much wider to compensate for the extra thickness.
My theory why the factory used a frame is that if it were a large 'unsupported'
laminated glass without the frame is that if you were to slam the door with the window in an open position it would/could possibly crack the glass.
Are yours rusted out,or is it more to do with looks?
Me? I quite like 'em!