It would probably be easiest if you did the wipers while the dash was out but I don't think it is absolutely necessary. You want to put some light grease in the tube for the flexible "rack" that drives the wipers. The only issues mine have is that they are very slow until the car gets going. I think I might have used grease that is stiffer than prudent when I put mine together. If your wheel boxes (I think that's the proper name for them) and your motor are in good shape, you shouldn't have any problems.
I forgot to add that your biggest problem will probably be to find wiper blades for the stock wiper blade holders. They are pretty difficult to find. The last set I bought were ANCO U-16R.
