I've got to agree with Globaliser - that is not enough time.

It'd appear that only easyJet flies between ORK and LGW.

I think your options are:
(i) reschedule your trans-atlantic flight
(ii) fly to London the previous evening, stay overnight
(iii) in order to fly from Ireland (this would be from DUB) to LGW the same day, I think it's only BA (and Ryanair) that could get you there around 9.30 or so. Even this would be pushing it.