Welcome to the site. I'm guessing your problem would be quickest answered by some of the locals. You can find them on this forum:
DM&FF :: Home
There are a lot of people on there doing their own projects, aswell as some fans of the Mustang II platform. They should be able to assist you in getting a proper diagnose, check of what you need, and how to go about obtaining it.
I recall there is a shop in the north of NL that has revisioned blocks for US vehicles as their primary business, but I can't recall their info. I'm sure someone on the forum will be able to throw you that info.
If you do join the forum, be sure to post up an intro thread with pictures. If you don't, be prepared to be asked for 'm
Hope this helps you out somewhat in solving your issues.