if you truley wanna block those ports, best way is to pull the cover, run a 5/16" tap in each hole, and install a rtv coated setscrew.. to truely block the port hole. Sometimes the cover plates leak, when just installing those as a remedie.
the Air Ingress, afforded thru the reeds, did actually prevent that back fire thing, by allowing fresh air into the exhaust, just past the actual exhaust valves, to burn off excessive fuel on decell mode, without backfires.. If they were removed, and there is a leak, its a tricky leak thing, as it allows pulses to puff back up, and into the valve cover (the reed is a one way valve, allow flow down, but not back up..)
if you did away with that all, the excess fuel, when shutting down the throttle, will accumulate, and pop, and backfire when the LEL (lower explosive limit) is reached, in the exhaust when the exhaust is diluted with enough oxygen, to explode. Usually down lower in the exhaust pipe, due to pulse.
Following you, keep up on it. I'm just trying to help at this point, not to be messing with you.(I think you know I apologized, and hopefully you realize I'm being sincere)
carry on,