here's an idea.
get back on a dyno and see what the a:f ratios are like now.
$60 it will cost you.
why risk it?
as said, if they played with the base timing, it will have a big effect.
I feel for your engine (and pocket) if you can actually HEAR the pinging.
think about it....
you are hearing a sound which is inside your engine..
you are hearing it over traffic, bonnet, sound deadner, exhaust, turbo...
all those noises and you can still hear it rattling away like a mofo..
so think about the actual damage you are causing.