What you've marked is correct . . . I've only ever used one base gasket (29 or 29a) under the powerhead, but go by the book . . . I'm kind of a hack when it comes to this
You might also be able to reuse 24 if it's in good shape.
The guys right . . . he should be able to have that powerhead off and the gaskets changed out in less than an hour. I would supervise if I were you. Make sure he cleans the surfaces well before he puts the new gaskets on given his history of mixing 2.4L and 2.5L adapter plates.
Also I would recommend getting more than one base gaskets (29 and 29a) Just in case you forget to put the shift shaft back and muck up the base gasket (it'll save you a trip to the store).