The 1947 - Present Chevrolet & GMC Truck Message Board Network

Greetings. I'm new to the board and also new to Chevy ownership. I've had a couple Dodge pickups, and a couple Fords. Most recently got rid of the dreaded 6.0 Powerstroke Diesel. I've never really been die-hard brand loyal to pickups, I always just went with what I liked. I've always loved these old classic Chevy and GMC trucks and I just picked up a 1970 K10 with a recently rebuilt 350 from a motor shop here in Oregon. It is in great shape with only minor surface rust in some spots. The bed has a couple of small rusted-out areas, but in a few years that won't be an issue. The truck has a C10 logo on it so I thought somebody added the 4-wheel drive along the way. In checking the vin, the first character is "K" which I've come to find out means it's actually a K10. Glad about that. Anyway, I'm having an issue with the front brakes which were converted to discs at least 10 years ago. The guy I bought it from had it for ten years and said he always had the same issue. When I bought it last week, the main issue is when the wheel is turned to the extreme left or right, the caliper and brake line are contacting the collar which causes the shoes to release which causes the brake pedal to go to the floor until I pump it back up. I am not much of a mechanic, but have a feeling I will be by the time this truck is finished. I instilled the help of my brother and we put new pads on it. The right side were nearly gone and the left looked nearly new. Looking at the issue we noticed that the bump stops were welded in place. Since changing the pads, the issue only occurs on hard left turns now and not on rights. Additionally, when driving down a straight stretch I applied the brakes and it pulls hard left. I flushed the old nasty brake fluid the other day and it's got clean juice in the pipes now. The calipers are both Delco, but are stamped differently so I'm guessing they came from different vehicles. We were thinking the easy fix would be to cut the weld on the bump stops and install longer ones to prevent the contact in the first place. This won't address the hard pull though. I also noticed that the lid for the master cylinder seems to be just a hair big and the master cylinder appears like it's leaked for a long time. It just spills out slowly. Is there a different master cylinder I should go with since the rears are still drums and require less fluid and a smaller reservoir? I know that's a lot, but just looking for some knowledged brake dudes out there.
Thanks.