Does anyone know if you Can use the rear glass window when getting a new top?
or does that comes already attached to the new top?

 

The glass is part of the rear curtain and is bonded to the curtain material. There is no way to "reuse" the glass only when replacing the rear curtain.

The rear curtain should be replaced along with the top in most circumstances. I suppose if everything was recently replaced and the top got damaged, then not replacing the rear curtain would be valid, but if the top is worn to the point of needing to be replaced, then the rear curtain is worn as well and should be replaced. The top has to be removed to replace the rear curtain, so it's a complete top job to replace just the rear curtain.

 

Is the curtain the same as the well liner or is that another piece of the puzzle?
Thanks!

 

The well liner is a separate piece that the top drops into when retracted, but it is attached to the same area as the rear curtain and the top sail panels. I opted not to replace the one on my car back in 1990 as it was still intact, and still is to this day.