For the 94? Is the window trim the same as the caprice?
I know on the caddy's if you swap mirrors you have to replace ALL the window trim, On the caprices all you have to do is change that triangle, drill the holes for the mounting screws to pass through and drill access holes behind the inner trim and then patch up that huge hole left by the 91-94 mirror.
Take a look and see if it's one big piece or if it's the small triangle. I might have the 95/96 trim and plates from the caddy if its that style.