You are kind of lucky to be in Canada because more 261's were used up there than in the states. They were used in full sized Pontiac cars instead of a V8 for a few years pre-'62. You may want to add an oil filter to one if it doesn't have it.
Email me if you have any issues, I worked all of them out in my '50 truck pretty well. I shortened my own water pump (used a new one and pressed the pulley boss down until it lined up) and used a foamoco water pump pulley that looks like it was stock. I added a Delco 10si alternator and converted to 12 volts. This is OPTIONAL! You can use the 261 with 6 volts if you use a 6 volt coil and use the 216 flywheel or get the 261 flywheel machined to use a 216 ring gear. I kept my 6 volt foot stomp starter by having the flywheel machined for the ring gear, and it cost me $50. I did it so I could use the 11" clutch that came with the 261, a 9" is too small. You could also find a 10-3/4" flywheel/clutch for a 216 if you look hard enough.
I used the big truck oil filter with my engine, but I had to relocate it to the front of the intake manifold because it hit the steering box. I used jiffyhose to connect it to the oil ports. They are big, 1/2" NPT ports.
I couldn't use the original oil pressure gauge adaptor with my block because of room issues so I drilled a hole in the top of the oil filter housing on the outlet side and threaded it 1/8" npt for the oil pressure line. I swapped in a later 60 lb oil pressure gauge into the gauge cluster and it looks nice and stock.
The fan on the 261 sits down lower than the 216's so if you have problems cooling you can add an electric fan, which is what I did. The mounts fit fine using the 216 bellhousing. You may or may not need to drill the front mount holes, mine came to me with them drilled. It's a '62 block. I blew my radiator before I got to drive the truck to see how it feels but it runs good at idle. I'll post on it this week when I get the new one in.
