Four or so years ago I purchased a short block from Chris at Engine Factory. I built it up myself and it still is running very strong. They have evolved over the years and now offer complete turnkey engines for Cobras. I know several people who have these, including a couple in England. Engine Factory has an excellent reputation.
Call Chris and ask for some references. Drive over and visit their facility and you will see what a clean operation they have. I believe they have a promo video also.
Also, they offer a one year warrantee on their engines, something that Ford does not offer.
Roscoe