64 brake master cylinder question

[RussTburb]

Hey guys, I am a 72 burb owner but love all these old chevy trucks! A friend of mine has a 64 c-10 pick up and it has brake issues. I replaced all 4 wheel cylinders and want to replace the master cylinder. I ordered one from the local Napa store and the counter guy claimed to know quite a bit about these trucks, he swears this is the right one for this truck. The part master cylinder I got looks completely different from the one that was on there. The one that I took off has a round reservoir with a spring clip to hold the cap on. The mounting bolts are horizontal. The brakes worked well until the master cylinder and wheel cylinder all seemed to fail at once. The new Master cylinder has a square recover and the cap is held on with a stud and nut. The mounting bolt holes are at an angle. The new master might bolt up but the push rod is too long and you can't even get the bolts started. Any one have an idea what is going on here? Should I just take the square the one back and get the round one? What year is that off of and how do I order it? Is the push rod that is in the truck (looks newer) adjustable enough? Oh I just remembered that the single line that goes to the brakes threads into the masters at different location too. Not that that can't be fixed. Any help you all can provide would be greatly appreciated!
Thanks for you time,
Dennis