I have a 123 on my 510 with a l20b with a weber 38. Your ignition map looks really close to mine I also do not run the map/vac i just zeroed it out and it is not conected. I run just regular unleaded 87 with no pinging even in the summer. maybe you got some bad gas it happens also i had a 521 with a l20b that would ping and deisel i just ran chevron 91 and it solved the problem.