67 chevy trailing arm suspension

[izonme13]

Hey guys, just picked up this rear suspension for my 56 chevy pickup. what Im wondering is, what is the weakest part of the suspension? Im going to run either air bags or coilovers. Havent made a final decision yet there. Kinda curious if the arms need to be boxed or if the front crossmember needs to be buffed up? Also Im using a 12 bolt rearend out of a newer chevy truck. What are you guys using for a panhard bar since it doesnt have the mount on the rearend? thanks in advance Robert