Howdy,
Actually a mid '60s truck bell housing will bolt to the stock mounts and to the 250. The 230/250/292 L6s and all the SBCs use the same bell housing bolt pattern, at least until 1988. Get the SBC truck bell housing with the mounting surfaces on an angle to horizontal like the original. Contact Langdon's Stovebolt on line for the front mounts. Tom Langdon has a 292 kit, but will modify it on request for the 250. Also you'll have to use a rear trans cross member for the 700R4.
It looks like I didn't read far enough in your post. You can forget the bell housing stuff I mentioned. You'll Need Langdon's front mounts and somebodies rear cross member and mount. You will probably have to remove the original bell housing cross member, too.
Be sure to get the detent cable exactly right!
best wishes,
Les
Last edited by Roadmarks; 11/29/2010 2:18 PM.