I swapped a 75 front crossmember into my 72. It is worthwhile, if you want: newer style A frame bushings (switch to poly is easier), quicker variable ratio power steering, discs, 5 lug wheels, easier to find lowering spindles, easier to find brake hardware, ect.
To swap, 12 bolts and the whole thing comes out. Things to get, with the crossmember: master cyl., brake proportioning valve, brake hoses, power steering gearbox, power steering pump (and hoses, as GM switched hose end fittings around a bunch), and all steering linkage, including idler arm & pitman arm.
The only trouble spot, the power steering gearbox will need to be spaced away from it's frame mounting .375" (3/8 inch). The extra width in frame rails (extra width is 3/8" on each side, and ONLY ahead of the crossmember mounting area) is the only change GM made in all these years. Your steering column will work, so will your shocks.
I'm swapping another front crossmember into my wifes 70 Chevy truck. This swap is a lot easier than trying to juggle front end parts around. E-mail me, if I can help.
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72 long fleet, 355 4 speed, primer, walnut goodies. Check out my web site:
http://shadetree72.homestead.com