What are the differences between the pre '58 261's and the newer blocks if any? Found a person with 2 complete engines and a few in pieces and boxes of parts including a valve cover with Pontiac written on it. Someone had used a paint pent to write 235/261 or 261 on everything but no years. This is a basket case sale of parts he inherited with a house purchase. There is also a 3X1 and a 2X2 intake and a set of split exhaust manifolds. Just thinking of a replacement for the siezed 235 in my '58 at a price lower than swapping in a 292.

I'm no expert, but as I understand it the '54 block was different (bigger water pump hole and thicker wall) but all the rest were the same.

I could be wrong though.

Canadian Pontiacs used 261's. They were all bypass oiling, hydraulic lifter motors.

Otherwise, The 261 changed in the same way as the 235 did per given year. The only major difference was that starting in '59 they made the 261's full flow. These engines have the larger 1/2" NPT oil line fittings.

The 235 has a 3 9/16" bore, the 261 is 3 7/8".

The parts that are unique to the 261 are the block, pistons & rods.

Pontiac stamped on the valve cover? That’s interesting as I’ve seen lots of Canadian 261’s and all the covers are plain. 1958 and later blocks in Canada have the cast boss for the oil diverter pin however this detail is not machined. A 1/8” NPT on the pin boss would make it a late Canadian car engine and if it has larger filter ports it came from a full flow truck. Absence of the pin boss would make it 1957 or earlier.

The valve cover is green and the Pontiac is written on it with a paint pen. I'm guessing it belongs to one of the disassembled engines. What I got for my $600 is 2 complete engines, 3 in boxes an Offy 3x1 intake and a no name intake for 2 Rochester 2bbl.s