Retarding the cam timing to reduce a miss is not a procedure I'm familiar with, it may be a technique used though??

It sounds like you covered all bases with the belt change. When the cams spring around they only ever close the valves, there's no chance of damage then, only when re-opening them to set the cams in the right position can they clash with each other. It sounds like you were careful in regard to that.

Did you use the upper engine cleaner at the same time? Clean the throttle body and/or change fuel filter?