I believe the Astrobee-D has a 117mm motor hook in it. If you used the hook with the appropriate gaps, I believe that the 124mm long 29mm motors will work. If you just used the motor tube and no hook (or baffle or brillo-pad mesh, etc) The motor tube is something like 250mm or so...Ive got an Astrobee D that Id like to stuff an H in. Whats the longest case that will fit in the mt with the baffle glued on the top?
The Aerotech rocket that is designed to take an H motor is the Sumo.http://www.aerotech-rocketry.com/customersite/resource_library/instructions/Kit_Instructions/astrobee_d_in_8-04.pdf
The instruction say the hook is 6 and 3/16 inches long, so you would be able to fit only a 29mm 120 case in there, which has no H motors. A 29mm 180 case would extend past the engine hook by about a third of an inch (its 6.8 inches long). Assuming you account for stability using additional nose weight and assuming that the kit can handle it, you could wrap masking tape around the motor and the engine hook to secure it.