I did the same swap, putting '76 parts in my '67 C20, about five years ago. There are a couple of differences you may want to look at before you start.
Some guys like to swap the entire crossmember, A-arms, tie rods and all. I took home the complete '76 suspension, but picked the pieces from both years that I liked the best.
There are slight differences in the '76 crossmember, but mainly just a couple of holes that can be drilled to line up. There is an angled piece on both sides, that the upper A- arms bolt to and this is bolted to the frame rails. The '67 is a large cast piece and the '76 is a lighter piece of pressed steel. They compensated by adding an extra piece on the inside of the frame rails. When bolted together, the frame rail is sandwiched between the two. Only one of those bolt holes line up, if I remember correctly. One has to be drilled and others elongated. The bolts through from the bottom do line up for both years.
I had taken both apart and picked the parts I wanted. I knew I wanted to keep the '67 springs, because the '76 was a big block. I kept the '67 cross member and added the '76 inside frame rail pieces for extra strength.
Either the upper or lower A-arm and ball joint is the same and fits both 67 drum and 76 disc spindle. The other arm ball joint fits only the '76. Sorry, can't remember which I used. If you were planing on using both upper and lower A-arms from the '76, you're good.
I don't recall that there was any difference in the tie rod ends. Someone correct me if I am wrong, but I thought that problem only came up on 1/2 ton conversions.
Be sure and get the sway bar. If you even have one, the '76 will be bigger.
The '67 brake line crosses to the passenger side on the back of the crossmember. The '76 lines go to the radiator crossmember, where the combination valve is located. The line to the rear of the truck from the combo valve, goes along the passenger side frame rail to a brass inline connector, just past the bellhousing. It's inside the frame rail. Your '67 has the exact same connector in the same spot. Unbolt all the lines from there forward and transfer to your truck. The flex lines go through the frame ahead of the A-arms, instead of behind as on the '67. I think there may have already been a hole there that had to be enlarged.
Be sure and check the lug sizes on the disc hubs. On the '76 I used, they were larger than the '67. I didn't want a mismatch or deal with getting new lug bolts for my aluminum wheels, so I replaced the studs in the disc hubs. Easier to change off the truck, before hand than dealing with it later.
Use the master cylinder and booster from the truck you take the suspension and brakes from. It would be stupid to use a Vette MC and have to fabricate parts for a mish-mash of parts. Using all parts from the same year truck will assure you that everything will work well together and make it easier to get replacement parts later on.
Take your time finding the right parts truck that is complete and the swap will be a lot easier. Either find a truck someone is getting ready to part out or keep visiting a pick-a-part till they pull one in that is complete and call in a buddy to give you a hand.
Hope that helps.
