This is a tough call. Thats why a contest prep advisor would be critical. Also, make sure you get someone that has worked successfully with tall guys if you can. We are harder to get ready (I'm 6'2 and used to compete).
For me, again I'm a tall guy too, and the body type that gains mass well, but also fat (ecto endo I never logged those definitions into the old memory banks!!). To stay lean I have to go low carbs and to get and keep size I need lots of protein. I also need cardio. Right now I run around 450 grams of protein, 100grams of carbs and a fair amount of fat. Red meat is critical for size. I also do cardio 4x per week.
I would say run 400-450gr protein, 200-250 in carbs and moderate fat. Very clean diet. A couple cheat meals per week max. I'd start cardio 4x per week. Now some may really disagree with this, its what I would do only. Again, find an advisor. My point was though, in my opinion, you don't have any time to waste in lowering bf and maintaining muscle. At 264 and 18%, your only holding 216pds of muscle at 6'4. You can't afford to lose muscle.