Timing a "unknown camed" engine....

Disconnect the Can to see whats what, and what to do. The Can can be mechanically limited in the backside by spacering the stop. I have used washers, slotted just wide enough to drop over the arm, and then pinching them closed. Just use your imagination.
While it's true that a big cam needs timing, it also needs idle-air.If you are throwing idle-timing at it, in an effort to gain smoothness, you may be sacrificing driveability, as you are discovering. I wonder if you are trying too many things at once. Firstly your A/F is pretty close right now, so leave it alone for a while. Then disconnect the Vcan for a couple of tankfuls, and concentrate on getting rid of the pinging. This will take aggressive driving from idle to 4000 rpm, no more. And not so much in first gear. The engine needs to be working hard.
I like that you have slowed the rate of advance down, very significantly. Perhaps pulling out 2 more degrees is all you need. I'm also glad that you are listening to your ears and other senses, and ignoring your head which is probably desperate to crank it up.