Hi AIMC --
My surgeon mentioned that he had a wide variety of graduated sizes in the OR so most likely they'd be along the line of the Hagars. The Hagar dilators, with their extended length, look like they could also be used for cervical dilation.
Did you see the Dilatin brand that Cliff has - https://www.adlermicromed.com/sapimed-dilatan/ -- they're very short ( 70 mm - 2 3/4" apprx ) and that would be more than long enough. There are only 5 sizes. One interesting point is they're filled with a gel that lets you either warm or chill them. Pretty sure I'd just want to start out at body temperature!
I'm pretty sure a "normal person" has an opening larger than you think. I remember the size of my stool back in the good old days before UC and surgeries. Of course, I never had cause measure myself back then! I'd bet a "normal anus" probably opens to around 25 mm.
As always, the J-Pouch Group has been comforting. It's nice to know that I'm in good company and will not be treading unknown ground!
Jim in Maine