All Alien arm sizes are compatible with all Alien body kit sizes. When selecting your Alien screw pack you must select the screw pack that matches the same size body kit you are purchasing.
Full build videos:
Basic photo build guide here
Info Minisite - http://aliens.impulserc.com/
Individual Parts Weight (5" Body and 5" Arms)
Complete Frame Weight (5" Body and 5" Arms)
Main portal for information on the frames is this thread...
(Camera, LED Ring, motors, props etc pictured not included)
Clips from FinalGlideAus & MrSteele!