stearing and crossmember help

The pitman arm on the power steering box will not fit the manual box, the splined shaft is larger on the power steering box.

If you are planning to use the steering linkage from the 74 car it will not connect to the pitman arm on the manual box becuase of the way they mount to the center link as mentioned by Redfish.

What you need to do is swap all the steering gear (steering box, pitman arm, idler arm, and center link) over from your 70 to the 74 k-member.

FWIW, dumping the manual steering and going to power steering was one of the best upgrades I have made to my 68 Barracuda. Completely changes the character of the car; takes it from being a slow responding boat to a quick and nimble handler not to mention no more parking lot thrashing.