Crossmember
 

whats the difference in the crossmember on a 67-72 to a 73-87?

Re: Crossmember
 

73-87 use a 9/16th U bolt to hold the lower arm cross shafts in.
To my knowledge that is it.
72 and up were equiped with disc brakes so a lot of pre-72 guys do the swap to get the discs. but that can be done just by swapping upper and lower arms, splindles, etc...
For guys interested in drop spindles there is a 3" option for 73+ but that can be done on any 67-87 1/2 ton 2wd suspension by using the 73+ upper ball joint. Pretty sure lower BJ is same 67-87 ( somebody will chime in if I got this mixed up.)

Josh