Your cheapest bet would be to research on how long ford used that particular bell housing so you can go to a junk yard and find one. It may not be from the same year, but as long as it has the same patterns you should be fine. You may be able to call them to see if they have any in their shop or in their field.
You can find repairs on transmission issues with your 1986 Ford truck at Dallas Mustang on Sandhill Road Dallas. Check for more details on http://www.dallasmustang.com/pages.php?pageid=4. AutoPartsFair.com also helps its customers find and purchase a recycled bell housing that is in good condition.