[Cdorp]

I inherited my dad's truck project, a 69 C-10 and this is my first tech post. My intent is to make it a clean, semi-regular driver, nothing fancy. On a budget and learning how to work on it myself.
It came to me with a pinched/cut rear brake line and no parts on the passenger rear drum. The front had been converted to disc long ago with what looks like stock height spindles and 1 1/4" discs. Also appeared to be the original MC. Braking was a lot of effort and anxiety.

I updated the master cylinder, added a disc/drum booster, and found the elusive drum parts. New flex lines x4, made new lines at rear axle and from MC to front T's.
Brakes work great and have the right feel for the first few times pushing the pedal. Then it seems the calipers don't release pressure, keeping the front brakes engaged. The pedal also gets really touchy.

The seal around the caliper pistons look worn out, the driver side has obvious cracks and a couple small pieces missing.
Am I correct to assume a caliper change is the best/likely solution?
Anything else to consider? Is there a potential compatibility issue with older calipers and adding a booster?

I'm considering the 73-87 CPP brake kit that also includes spindles, ball joints, tie rods etc. Most of mine show signs of wear. Probably do the shocks while I'm into it too.
Which leads to ride height question for spindle selection:
Any experts here able to confirm I have stock height spindles(see pics)?
I'd like to remove the rake from the rear eventually. Overall, I don't mind the stock height, but bringing the front down an inch or two and the rear to complement would be ideal.
Can I lose 1"-2" from the front by just changing to lowering coil springs if I keep stock height spindles?
I also inherited my dad's boat (See pic) How can I drop the rear height with leaf springs, while maintaining towing capacity? Is this possible without cutting the frame + c-notch?