Is this a 351 Cleveland?

Its a 351W.

In a Pantera, one aspect of the engine most visible is the rear of the intake manifold, which must conform to the shape of the rear "valley rail" of the engine block. So perhaps the attached picture shall help you identify engines in the future.

Also notice where the rear of the intake manifold seals against the block, there is a gap between the manifold and the top edge of the bell housing. You can see about an inch of black engine block between the two castings. This is about the same for the 351C (9.2" deck height) and the 351W (9.5" deck height). But the little 302 (8.2" deck height) does not have a gap in that location, the top of the bell housing is flush with the rear of the intake manifold.

This engine is also equipped with in-line valve 302/351W style cylinder heads, the rear of the 351C cylinder heads are larger and rectangular in cross-section.

Thanks for that!! Makes senses.
Maybe I should do a new thread but would this hurt the value of the car in the Pantera world swapping engine for 351 Windsor?
I had other cars like Jag Etype or 911 and it usually hurts the value...
Thoughts?

I doubt it would hurt the value. It lessens the originality but originality isn't key to the value of the car in most cases. Only if you're looking to keep the entire car original for its investment value would this be an issue. Having a Windsor I'm sure would be preferred by some buyers as it allows for more flexibility in modifications e.g. increasing displacement.

In terms of stroking either motor for MORE displacement, I believe there are after market kits/mods that equally address BOTH the Cleveland & Windsor engines.
In FACT with the Cleveland's Superior head design vs the Windsor, a Cleveland's ability to BREATHE lends itself MORE favourably to increased displacement.
Doesn't a 4V Cleveland head flow almost the same numbers as a 460 Ford engine?...Mark

Three more easy engine ID tips ....

Cleveland heads' valve covers have 8 bolts each, Windsors have 6.

Cleveland block has a port for oil pressure sender in the area where the manifold bows inward in the above photos, Windsor blocks do not have this port.

Cleveland thermostat is in the block, Windsor is in the intake manifold.