I just measured mine and grate is about 6" from top. I'm thinking I could just drill some holes lower and use my UDS but I thought the grate had to be a certain distance from fire basket.
My vote would be for another UDS...maybe do a Big Poppa so you can grill sear as well as smoke. The double barrel would look cool but not be near as efficient.
Turkeys/chickens will fit spatchcocked fine or upright with flat lid if your cooking grate is down to about 8" from the top.