Any chance you could take some picture of the throttle linkage from the engine to the front of the firewall.
i need some info as I'm not sure if my Superliner's throttle linkage is from factory or the previous owner somehow decided to change. It's a cable right now.
Same problem I had. Took mine to get rodded out and was told the core was shot. They quoted me 800-900 dollars for a new core, (I think they're 4 row cores). That was about 5 years ago. Looked around and tried to find one but didn't have any luck. I ended up using a universal aluminum unit from Griffin Radiator. Had to fab a whole new cradle to mount it in the Mack. The only original pieces I used were the pressed sides. Took a good bit of work but seems to cool the 427 just fine. It will idle all day in the summer heat at 170-180. I'm sure there are places that could have repaired it but, I didn't want to fool with shipping it around the US.