JB1 to JB5/JD3 brakes?

[83Stepper]

So doing some things to the truck and was able to finally get the old girl registered and titled and ready to go on the road this week. Took it for a 5 min ride down the road to the local clam box and noticed something funny with the brakes. Pedal feels fine for about 3 inches or so then gets really stiff afterwards and brakes felt like they'd lockup and stick. Pulled off the front tires and noticed both sides have 1.25" rotors. I know they originally came with a 1" thick rotor. So I'm assuming the previous owner did some swapping of things around in the front end. Truck was originally a 4.1 I6 with a 3 on the tree, so I knew I'd find more things that weren't stock. PO at least was thinking of stopping with the higher displacement and probably thought with the heavier rotors they'd get more stopping power. Know it's the JB1 because the rears are still the 2" shoe.

TL;DR version: Has anybody swapped from a JB1 rotor to a JB5/JD3 using the stock master and calipers? Rotors are stamped 1.215 so I know they're the 1.25's. Calipers seem to be very snug when I pulled them from the rotors with the pads loaded. So I'm assuming the stock JB1 calipers are still installed hence the reason the pads are so tight to the rotors. So can I just grab a set of the 1.25" calipers and toss them on without creating too much of an issue or would I need to perform a full overhaul of the brake system? Might just end up going back to the 1" rotors and be done with it, unless the spindles were swapped as well...