261 Truck Engine

[chris vickery]

So Grant, externally what is the best way to decipher the mystery?
To surmise, the Chevrolet truck 261 used a 9717 block with '50 heads although the 858 head was a common swap.
The Canadian Pontiac also used the truck 9717 block with 858 as standard equipment.
Is there a definitive Pontiac identifier on a true Pontiac engine?
I understand the internal differences, eg solid vs hydraulic lifters and aluminum timing gear vs fiber.
I talked with the seller and he has no idea of the history on this engine.