1974 Duster restore or not

I heard that before about the wiper seals I think that's where most of the water comes in. Is that a big job? How do you get at them, under the dash? The dash has a rust hole at the left corner that needs a patch welded in. The engine is out and the new one is waiting for parts so that I can reassemble it. Fifty bucks for a slant six in the crate! What a lucky find. I'll post some pics of the progress. I alway's wanted a vitamin C Duster.