Hmm, I think all of the big coasters will be either out of the question or borderline at best. He may fit in the one I did with R [it was a newer, straight up a hill coaster] but it was painful for me. I don't think he would fit in the looper, the great bear or the other vertical coaster that R and I didn't do (I couldn't even get half in the test car for that one).
275 is lighter than me and he's taller so I don't know, he may have better luck
if he's not claustophobic ;-) [because he felt squished]
I couldn't take anything but very shallow breaths on that one coaster because the bar was compressing my chest [the very fast up the hill one]
If they have kids, it would definitely be worth the trip. Just not if they're going specifically to ride the biggest, scariest coasters.