*should* be a bolt in -- if somebody already boogered the upper radiator shroud when they moved the radiator forward to accommodate the 235's water pump. And changed your engine mounts... and you already have the adapter plate for your water pump ...
After 1954, the 261's were built to go in the Tack Force and later trucks, thus they have a lower water pump than on the engines built for Advance Design trucks. You will probably need to get the adapter plate to raise your water pump to get better cooling (otherwise half of your fan disc will be below the radiator.
Also -- the Advance Design trucks had the one engine mount at the front (under the timing gear cover) and two at the bell housing. That '60's 261 will most likely have engine mounts on the sides near the front of the engine. Not too bad of an issue if you are going to rebuild the 261 anyway -- just use the plate off the front of your 235 to switch the 261 to an AD engine mount. Otherwise you will most likely need to fabricate some sort of an engine mount.
For more info on rebuilding a 261, check out our tech tip we wrote when we rebuilt mine for my '49 3804.
Rebuilding a 261 for use in an Advance Design TruckBut once you have all this laying flat, its a great upgrade.
John
