Rear suspension for the '68 was covered here:
https://lateral-g.net/forums/showthread.php4?t=18200.
Richard Ehrenburg is an automotive engineer and tech editor at MoparAction magazine. He has some well thought out objections to the AlterKation setup, which as I recall he views as a drag race suitable setup with no real world durability history. This may have changed in the last couple of years.
My first car was '69 R/T Charger 440/auto/3.23 posi I bought for 400 USD from a friend needing to get his girlfriend out of jail. It ran like a scalded ass ****in' ape after rebuilding the engine, and had enough top end to bounce the needle up around the 150 mph mark. I don't think it was anywhere near that fast, but trying to time it on the flying mile I got an honest 130 or so and could run away from about anything on the road in Montana back in those days.
Pretty scary ride on the wide/skinny tires musclecars had then.
I still own it and it is finally headed to the rotisserie for a teardown and rebuild. I have no need for an exotic engine swap or brake setup, or to get rid of the rear link steering, and I don't need a ProStreet look underneath, so 4 link or tube frame is out.
What I intend to do is go as far as I reasonably can with a stock type suspension setup, doing all the fabrication myself. I hope to try and approach the skid pad numbers of my dad's Z06 at a fraction of the cost, by stiffening, balancing, lowering what I have as much as practical.
What I want to do is give the car the braking and handling that it's potential power and speed deserve.
I was fortunate as a carpenter, mechanic, and now as an oilfield mud engineer to have worked around some very smart people. I found two things: I learned a lot more by listening to intelligent people who have walked the walk than I did by talking. I also learned never to discount anybody's practical experience, even when it disagrees with what I am pretty sure I already know.
Good luck, Mike