Champion Radiators in an A-Body

you know, i couldnt get a good answer on tube size or core thickness from the guy that sells the champion radiators on moparts. he was giving me dimensions to the top tank never answered what size tubes they use. when i told him i had way more room he did tell me the 3 core was only 3/8" thicker and i could send it back if i wanted for the 3 core. i didnt really get that, the tubes look like 5/8 or 3/4 how the hell could one more tube only ad 3/8". again i asked what size the tubes were and never heard back. so i just kept the 2 core. i probably will get another 26" 2 core from him for my dart the howe rad from 2000 is starting to leak from the tubes.