|What you have is normal and what you have done is right. The casting at the foot of the mast sits in U-shaped channel with s/s pins fore and aft to locate it securely. Most people don't seem to shim the mast to prevent twisting, but I think it's a good idea. One additional thing you can do is to make the rubber tubing in the spreader sockets a very tight fit. The less your spreaders move fore and aft, the less your shroud tension will vary from tack to tack.
C&C 27 Mk IV