Thanks. I still haven't found the right side yet (but I admit I didn't look too hard today). I pulled the left side, came loose which a mighty crack, so loud I thought the plug had broken, and then when I saw that stubby little stem I was sure. Add to that that nothing what so ever came out, I knew I'd screwed the pooch. Tried the screwdriver trick and found it was just a crud plug, and got the left flowing freely.
What I opted to do for now was just do extra fill/drains. Have done five today (radiator was ready at 9 AM). On the fifth drain the water was running pretty clear and estimate I was getting about 3 1/2 - 4 gallons between the radiator and block.
I'll look in earnest for the right side tomorrow now that I know both sides are the same. I'm thinking the right side might just be on the back side of the mount, since I didn't see anything similar in front of it.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.