Yep, leave out the grapefruit proper and use a blend of Centennial,Amarillo and a little Chinook, late and dry. Bitter with Chinook. Though you could (I suppose) add the zest of a grapefruit (NOT the pith, zest only !) into the keg in a nylon bag with a string and leave in until it tastes where you like, then yank it out. It would work.
As for the grist, I'd go clean to accentuate the citrus. Maybe 95% 2 row, 5% C40. 1056/001/05 for yeast.
~ 68-70 IBU, OG 1.063ish. Mash 150F.