I'd do 1.5 oz challenger at 60 minutes, 1 oz EKG at 15 minutes, and 1 oz EKG at flameout.
I also don't think that 1 lb Maris Otter is going to be able to convert 1/2 lb Flaked Maize. I'd dump the maize and bump up the M.O. a bit to compensate (if you feel the need).
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