Its not hard to replace the babit 235 with a 261 but here are a few things I learned.
There is some planning to do before you start. Mainly around what you are going to do with the water pump, and whether you are going to convert it to 12 volt.
Water Pump.
I thought I could just install a short shaft water pump and make a new shroud. Nope, the fan hits the lower radiator hose. The choices are to move the radiator down a few inches, or purchase a water pump adapter plate.
I chose to purchase the water pump adapter plate. I didn't want to hack away at the radiator mount. this also allows me to use the stock lower radiator hose and hopefully the stock shroud. the waterpumps have different diameter outlets. the 235 has a smaller outlet.
adapter plate instructions are here
http://chev235guy.blogspot.com/Crank Pulley
Since I went the adapter plate route with the wider fan belt, that means I need to fit the 235 crank pulley onto the 261 crank. Some light honing of the crank pulley was needed to get it to fit. I left it out in the sun to heat up as well. By the way, the 55 crank pulley wont fit on the engine in the truck with the 235 engine mount. it hits the front engine mount. The 55 pulley has a bigger diameter.
Fly Wheel
I am now painfully aware that '55-'62 flywheels use a ring gear with 168 teeth, and must be used in conjunction with a 12 volt starter. All 6 volt flywheels have 139 teeth on the ring gear. I left the 55 flywheel on the 261 so I guess Im going 12 volt. i think the flywheels are interchangeable, so if you wanted 6v systems, you needed to switch flywheels before installation. i didn't think that far ahead.
Generator
the belt width is different between the 55 generator and the 46 generator, so I have to switch the pulley and put the wider pulley on the 55 generator (12 v). I guess I could have converted the old generator to 12 v.
Oil Breather
The oil breather that comes out of the passenger side of the block are different between the 55 261 and the 46 235. The 55 has a breather hose connection. Its a simple replacement to put on the 46 oil breather.
Valve Cover
The 55 261 has a breather hose connection at the back of the valve cover. There isnt anywhere for that to go on my 46 truck, so my solution was to run the 235 valve cover until I get a wayne kit. 46 has center hold downs, the 55 has 4 bolts around the edges.
Starter
because the flywheel issue, i have to run the 12 v starter from the 55. the o.e.m. p/n for the twelve volt starter is 1107634 that is Napa p/n WIL91013684
Thermostat housing
i had to use the thermostat housing from the 46 235. the hose diameter is smaller on the 235 thermostat housing, and using the 235 housing allows me to use the stock upper radiator hose.
Manifold mounting.
my 261 came with dowels, not studs, on the outermost mounting for the exhaust and intake. that seemed like a recipe for leaks so i replaced them with studs. Dont know if those dowels were factory but it seemed bad.
Oil filter
i decided to not run an oil filter. i am running fenton headers, and the oil lines to the external filter seemed like a bad idea next to the exhaust.
Fenton Headers
the steering box seems to be in the perfect location to interfere with the dual exhaust on the 46 2 ton. i probably will run the back header pipe behind the steering box, and the front header pipe in front of the steering box. The front would then have to go under the steering box. i will fabricate a heat shield under the steering box. i know this topic isnt engine swap related, but is part of the install process for me.
Gauge hookup to the block.
the water temp gague hooked up in the stock location of the head. im running an 848 head off a late model 235. i didnt want to run the oil pressure line next to the headers, so i moved it up to the head on the passenger side near the distributor. we will see if thats a good idea or bad idea once i start it up.
Front motor mount plate
i had to switch the front motor mount plate. thank god i had to do this, as the large timing gear on the 261 was cracked. i was bitching about the amount of labor to take off the pans, pullies, cam covers and mounting plates but thankful i found that cracked gear. i switched the rear seal while i had the pan off.
summary
figure out ahead of time what you want to do with the water pump and 12v vs 6v. keep the old engine nearby, you will need a lot of parts off of it. it also takes a bit of time to switch out the mounting plate. its those dang reverse bolts in the timing cover.
