You were overheating. And you are putting $ and blood into a new motor. Do this for sure. Trust me. Take the radiator and have it rodded out. Even if the core won't rod, have them recore it before you buy an aftermarket. There's a 3 row core that will fit. Your tanks are three times as thick as aftermarket tanks, which all have the midget filler cap, too. And rod out the cat...

Not responsible for advice not taken...