Need to get new springs on my 68 4 door, and may crank up the torsion bars a bit, or buy thicker one

I am already worried about too much ride hieght gain and too stiff springs harming the ride- why do you suggest the 6 leaf? I am guessing the rear end is currently sagging about 2-4 inches lower than stock, and these raise the rear end 2 inches according to the description, which could mean as much as a six inch lift from where it is now to the rear. The six leaf version is for the BB dart after all?
Nah, you'll be fine. Your previous description of the cast of characters who may ride in your car will settle the ride down after a time.