Outside vent cap replacement

Hi
Realized a new kitchen exhaust fan I bought requires a 6" round pipe (3 1/4x10" not an option given current bulkhead). The house has a 5" round pipe currently installed that terminates to a 3 1/4x10" adapter, then a sleeve to get from the adapter to the exterior wall and then the exterior 3 1/4x10" vent cap.

This cap is no longer functioning (air, birds, bumblebees, mice chipmunks, etc getting in) so I want to replace it. While at it I wish to replace the 5" pipe with the required 6" pipe. I'm not a fan of all the transitions going on so I was thinking about going straight out with the 6" pipe and getting a wall cap that will fit the 6" pipe.

However, there is a hole cut into the brick wall to fit the 3 1/4x10" cap and this brings me to my question. Anyone know of a system to cover the existing hole and then cut out for a 6" application? I know I can replace the brick and start over but I was looking for a less intensive solution. Kind of thinking about some kind of outdoor friendly plastic piece that I can affix to the wall or a cap that is wide and long enough to cover the existing hole. Thanks

 

I see no reason to change the vent cap to 6" round, just installing a new 3.25 x 10 cap is good.
I install all kinds of vent hoods and microwave hoods. Adapting from 7" round or 6" round to 3.25 x 10 will cause no problems IMO.
I would use a 3.25 x 10 x 6" round adapter and be done.