The 261 has siamesed cylinder walls but the 235 doesn't. That may be its only disadvantage since the flow of coolant to the head isn't as good.
I love my 261, I used it to pull a bed full of rocks (about 1500 lbs) up the Sunset hill at 55 mph yesterday and it didn't even seem like there was a load in the bed. My old 216 couldn't make it up that hill without slowing down, but the 261 was still pulling a strong vacuum. The temperature never went over 190 (with 180 thermostat). Nothing else about the truck is changed, same gear ratio and exhaust pipes.
