Good Day All

Finally got the '68 Bee out for a spin and some fresh gas. (only filled it three times last year).
On the way home from town, whenever you lifted out of the throttle the car acted like the brakes were on.
The car is a 68 Suberbee with a disc brake conversion (Finelines). This was done a couple of years ago. I had problems then with a defective proportioning valve.(The front brakes would not release). The valve was replaced with a O.E. type (non-adjustable).
Tonight, I jacked up the front and attempted to spin the wheels by hand. You could turn rotate them, but not able to spin. I loosened the master cylinder from the vacuum chamber, which removed any load from the push-rod, but the result was the same. I just checked again after the car has sat for a couple of hours. The drivers side will spin, but the passenger side is still tight.
The car has the newer style calipers (single piston), and silicone brake fluid. the hoses feel O.K. (no soft spots or bulges)
Any thoughts as to what is going on?
Thanks to all who respond.