Currently doing so in my 63, there are alot of forums based on the swap, I am doing a 4.6 and doing a rwd conversion on it using a 2.8l 700r4 tranny.  People who have done the swap have reported gettign 25-26 mpg on big boats such as ours... that is why I am doing it.  check out a site called 
www.chrfab.com or .net  they have everything u will need, and some badass billet valve covers and a forum.  use a stand alone ecu