Piece of cake once I had the dimensions, you can't use the same holes, either of them. I was at the assembly stage, so everything was painted, found some neat little vinyl plugs to close the old holes and drilled some new ones. No threaded holes where I needed them so I used some sheetmetal screws that have a drillpoint on the end, like the ones they attach metal buildings with, hexhead. Since I have the '66 windowframe, my WS is about 3-4" shorter than the later models that don't have the cowl vent in the WS frame, so had to cut, shorten and weld my wiper arms,PITA. It works and looks fine, IMHO
Good Luck,
Ed