Looking at buying a 68 ,the worst problem is that the rear window metal is real bad around the whole thing, is this a hard fix ?

 

I know you can but the bottom section but not sure in the rest but I have seen them cut out and weld in parts that could not be salvaged.

My worry is, if it's that bad I would want to tear out the rear seats and side panels and see how bad it is down lower. Not just trunk pan (where shocks mount) and floor pans . Depending on where in the US the car is RUST is the enemy.

Read some of of the threads where the members are or have started a rebuild, that will give you an idea.