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.
