Optoma projectors use lots of different IR protocols.  I'm reasonably sure that the GT760 uses NEC1 Device 50.

The RCR503BR code list only has one Optoma code: TV 1348, and that is NEC1 Device 51.  So I'd be surprised if it will control your projector.

I don't know of any remotes (other than the Latin American OneForAll 7340) which has a suitable setup code built in.  The cheapest way I know to get a remote to control your projector would be to buy (or find) a cable remote (most obvious is the Comcast 3DVR remote) and also buy a  $8 JP1 flash cable.  You can then use the free RMIR software to add the needed upgrade.  But it takes some time to get the JP1 flash cable, and some learning to use the JP1 software.

Or, buy a $24 OneForAll OARUSB04G, and use the Simpleset.com site to add setup code TV 4075.