Welcome to the forum. Your problem is a puzzler. Obviously the stock 427 cast iron exhaust manifolds would fit with the stock starter on a stock car, and the bellhousing you have can't be repositioning the starter because then it wouldn't engage the flywheel. So the stock starter really should fit. Failing that, if you got one of the "clockable" aftermarket starters (Powermaster 9506 or 9606 or a Robb McC starter), you should be able to rotate the starter/solenoid around to make it fit the manifolds.
FYI the more expensive XS Torque Powermaster starter is not "clockable", but the cheaper one is, at least according to the Summit web site. Go figure...