68 kframe vs. 73 & up
I like the spool k-frames, for several reasons. I like them so much I even cut one down to fit in my '63 Valiant.
1. The motor mounts wont break and cause your motor to lift and cut your upper radiator hose. But, you can get around this with some aftermarket biscuit motor mounts with a screw that makes it impossible to tear the motor loose.
2. The swaybar is much tighter to the chassis and doesn't limit front tire size like the earlier k-frames where the sway bar mounts out in front of the k-frame and has longer arms than the later one. The later swaybar is easier to mount, and with it's shorter arms it is much more effective for the diameter (although this might be a wash as the later bar mounts to the lower control arms farther from the lower ball joint, which reduced the effectiveness). At the same time, you can now buy aftermarket earlier front mount swaybars with a bend that give tire clearance.
3. The 73 and up k-frame does have a different idler arm mount, that is much more effective. The idler has a through bolt instead of mounting on a stud to a plate. This makes the mount much more effective, enough so that I think it is the only way to go. There is no work around for this on the earlier k-frames, short of cutting the idler arm mount off a later k-frame and welding it to your earlier one. No thanks.
If you want the car to handle, you are going to have to deal with deflection in your steering if you run the stud mounted idler.