Take a look around the lines, calipers, and pistons to check for leaks. If any leaks are present, fix 'em.
I've noticed a lot of new stuff. It's possible there's some air trapped in the lines somewhere or in the calipers, which would explain why it takes so much force to brake effectively. I'd recommend going around 'em with a one man bleeder and check for air in the lines.
Of course, the braking system is only as good as the pads and rotors you have. Pop the calipers apart and pull the rear drums off, then give all the pads and shoes a quick scuffing with some sandpaper, around 500 gritt or so. That should remove any contamination or glazing if any is present. Of course, if they're worn, replace them with new pads/shoes.
Also, make sure there's no kinks in the lines either.
One last thing. Ensure the caliper guide pins are well lubricated. If they can't move easily then the calipers themselves will have a difficult time doing their job. I'd strongly recommend either silicone or a packet of the caliper guide pin grease you can find at auto parts stores, as true petroleum based grease will rot the rubber over time.