I think the 76 tranny will go into the 67 body. I know the tunnel isn't as big as later cars but I think Barry Parkinson has made the switch. You may want to try reaching Barry at;
[email protected].
You may have to work on the tunnel with a hammer, I believe it was made bigger to make room for an automatic transmission.
You didn't provide enough information on the 67 body. Does it have an interior to include dash with gauges, seats, panels and carpets, steering column and steering wheel, wiring harness, front crossmember, gas tank and radiator?
I mention these items because you will have to source most ot them if they are not in the car. It can become a rather expensive swap if you have to purchase most of these items. Sounds like it will also need painting
I believe the front engine plate will need to be replaced with an earlier plate and motor mount brackets. You will need a chrome bumper type crossmember and steering rack. Barry may have some information on that, I can't remember which way he changed things. The rear should bolt in without worring about lowering, most of the raising on later cars was the locatoin of the spring and shackle mounts. Most of the change in the front height was in the crossmember.
I mentioned wiring harness because if the 67 doesn't have one and you have a 76 harness there is so much difference you may never get it working.
In either case you may need to buy a new harness.
In short the change can be made but to have a nice car it may cost more than buying a good running car. That's my opinion.
Clifton