Joe,
The adaptor was indeed #502. The inlet ports are sized for -10AN o-ring fittings. Below is the link to Holley's web site.
Earl's Theromostat
I used 45 degree hose ends, and the part number was 844510. I believe that the 90 degree fitting would be 849010, according to the chart on the attached link.
Earl's Hose Ends
I found the AN sizing to be a little confusing, but found the following chart to be helpful:
AN Sizing Definition and Chart