The only trucks these 261's came on was the larger ones with the big radiator. But so far, both casting number sets (one that is the same as Tims) show the outlet is the 1-1/4" ID (just a tad less) like the 235. I am looking forward to the pics so I can show there IS one with a larger diameter.
When you think about it, it's probably functionally moot because the restriction at the head is the same. Since smallest orifice determines flow, the 1-1/4" one is probably just fine except radiator hoses are a pain to find.
On your radiator, would the old one fit in your truck? I did two things to make sure that Roy's suggestion that the siamesed cylinders needed better cooling. I got Dave's adapter plate to move the fan to the center of the radiator, and I got a modern cored radiator that looks like the original from US Radiator. Pricey, but I do not want overheating problems.
