The 36 (designed by Alan Gurney, not Bruce King, btw) is a much newer design built into the late 70s, the 37 (indeed designed by King) seems to have been replaced by the 36, so the 37s will be older.
The 37 appears to have a spade rudder, while the 36 is skeg-hung, pros and cons for both of course, depends on your preference. My observations are that the 36 does not back up well under power, but she's certainly not alone in that category. Most 36 owners seem very happy with them - they are a timelessly attractive boat.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)