conical washers??

I wouldn't pay $50 for a set since you can get a whole slant engine almost free. A co-worker had a slant in his truck in the early 1990's and had to buy a new set from the dealer because his manual said to always use new washers when installing the manifolds. Never heard that since, and I told him I never did and couldn't think of any reason that is necessary, but it suggests that dealers would have stocked the washers, so perhaps some still have them. Your local dealer can search the country for stock. Be sure to review the article on how to install them on slantsix.org, since it isn't intuitive.