The manual for the zero you may download from: dz185cdizero.pdf

Anything on the outside of engine to confirm you know of?
I converted to the zero-version myself, replacing the piston only. So I do not know if there is any marking on the outside of the engine. To be absolutely sure you have to compare the pistons (nitro vs. zero).

Running nitro in a zero engine would not be good, right?

Some has used 5% nitro with success:

https://www.brueckner-aviation.com/e.../carf-valiant/

The manual for the zero only states 0% nitro.

If it is a zero, does Klotz oil have any blends of oil that are good for a fai blend?
Sorry not familiar with the Klotz oil.

Good luck!

Arnstein