I would assume that with shocks removed and suspension hanging at full droop the hose would still have slack. As I understand it the earlier 69ish and older with the breather on the hump had a longer hose and the later year had a shorter hose.
How about a photo of the bracket in place
according to Rock auto:
67 rear hose is 14.6" long
71 rear hose is 13.7" long ( looks to be same fittings as 67)
74 rear hose is 14.5" long but has an integral distribution block attached
can you supply a photo of the mounting bracket on the body, perhaps you have it installed upside down or the like?
found this 70-71 parts book
is this your routing? If your "T" was facing to the drivers side, might be an issue.
70 - 71 parts book shows 3461728 is hose
Ebay listing from Brads NOS shows 3461728 is about 13.75" (AND get a load of the price!!!!!)
NOS Mopar 1971 Plymouth Cuda Dodge Challenger R/T REAR BRAKE HOSE pn 3461728 | eBay
Also are you using stock springs and shackles?
any chance the bracket you are using is not the correct one?