Here is another example of the typical Rushton oarlock. Sorry about the oblique angle, I'll try to take another when I'm at work tomorrow.
I haven't seen sockets like that on other Rushton boats, I'm not convinced it is not a later addition.tapered sockets would be very unusual, and pose a particular problem. If the shaft of the oarlock is not machined just right, they will rattle if too loose, and if too snug, they will lock up in use - just think of the Morse tapers used in lathes for example. I have only seen one set of rowlocks with tapered shafts, and the socket was fitted with a ball bearing insert.
The Morris oarlocks are very common - they were mass produced by outfits like Wilcox-Crittenden. I've got at least a couple of sets like these in different sizes, and will try to remember to photograph when at the shop.
Dan