I helped someone do it on a different brand hull.
I don't know whats inside the gunnel in your case. You need to stare at it a long time to figure out which angle and length of rod holder you can fit where. Take into account the flare of the hull.
If you want backing plates and bolts, you probably need to cut in and mount a 4" or 6" access plate in the gunnel bulkhead.
Position it so your hand can access the bolts easily. If you put 2 near each other you can get 2 with one access plate.
expect to drop nuts....
To keep water out of your foam, you need to get rod holders with drain fittings. Then plumb some tubing straight down and go out the gunnel bulkhead(inboard) thru a "Push in, barbed drain fitting" TH marine make some in different sizes. This will drain the rod holder to the weather deck.
They should put them in standard on every Grady...
never enough rod holders....good luck