273 Can't get too much timing - confused

It was Taylor's Ridge near Summerville GA. Not too high, about 1600 feet. But high compared to Rome, lol.
I'll need to borrow a compression tester from a parts store. I don't think the engine has ever been apart and it's somewhat tired.
I backed the timing down to about 17* after church this afternoon. I'll check the plugs again after I put some miles on it.

Thanks!!