Why not bolt it together, get a good file and file it flat, sit the sumpplate on or bolt it on with the good bolt, mark the holes drill and tap them, a tap would only cost a few $ . The sump plate doesn't have to be perfect, just flat so it seals. The top where the cyl bolts on needs to be square to the crank as well as flat and can also be done pretty easily with a file, an unmatched set of cases can have the cyls tilted to one side, you need to check it and even it up if necessary.