I’ve done a rip cap several times on a gas grill. I’ve used indirect heat each time. I have the Charbroil/TEC grill with two infrared and two flame burners and so I put it over the two inside burners and use the outside flame and outside infrared burners. Going more toward medium allows the marbling to melt into the meat. Both Bryan and Bill have told/written that to me. I have also started on the grill and finished in the oven. Think about adding some thyme to that rub.
I’ve done two a couple times on our Weber Summit gas grille. I grill them on all sides, and then turn off the inner burners and finish until around 130F or so on indirect. It takes somewhat longer than one would think.