Buc,
I just replaced that same bearing on my ’56 RD-18 30hp. The bearing number 20-52 represents the bore and outer bearing diameters in millimeters. Bearing depth/thickness is 15mm, so full number is 20-52-15. Doing a google search, I found a corresponding ball bearing is either SKF bearing #6304 or NDH bearing #3304. Photo of mine enclosed.
Bob
1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1955 Johnson QD-16
1957 Evinrude Fastwin 18
1957 Evinrude 3022
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20
1982 Evinrude 25hp
“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."