I would have to say it will be cheaper for you to go for a set of world ST heads, they have plenty of flow potential and in the long run they will be cheaper than the price of 461 +crack testing + seats + macining+new valve guides And the clincher is they are brand new and not 40 odd year old iron. If those 461 heads have still got there stck port shape ( have not been ported ) and are not cracked, they could be BIG money to the right person.