K member swap

The '73-'76 K member has some advantages over your '67. The sway bar mounting system is much stronger, the steering and brakes are out of a B body, and the engine mounts will not separate and let the engine move around. New parts are a lot cheaper and more commonly available than the '67.
How you do the engine swap depends on how you get your disc brakes. If you find a car with discs on it, take the K member too. If it isn't a V8 K member, big deal, Schumacher has a kit for that too. If you get your discs as parts from a seller, keep your '67 K member.
If you move your battery to the trunk, the weight difference between the /6 and the V8 is pretty much offset, so you may not need torsion bars. Crank them up a little first. If they won't sit right for you, then change them.