Hi!
You will need the following special bolts for your A10/A7 alternator chain case. I found out the hard way that there is nothing available in the BSA emporium and no NOS. It’s trial and error. I assembled the chain cases and the crankcases using the following:
a. One 5/16 inch screw with ¾ of an inch of whitworth thread. This needs ten thou taken off the diameter of the screw head to fit into the outer alternator cover. This goes from the outer cover right into the crankcase.
b. Two ¼ inch screws with ¾ of an inch of whitworth thread to fit into the outer alternator cover. These go from the outer cover right into thr crankcase.
c. Two 5/16 inch screw with ¾ of an inch of whitworth thread which secure the inner chain case to the crankcase.
d. Twelve ¼ inch screws, ½ inch long, completely threaded with whitworth thread which secure the outer to the inner chain covers.
The late B31/33 single alternator chain cases are completely different and require major surgery to fit to the pre-unit twins. They have virtually no parts in common with the A7/A10 alternator chaincases
Hope this is useful.
Martin