RLM 65 (1938) vs Russ. AF Grey N.8

How close are they?

ΔE 7.3, close: similar, with a visible difference side by side. Russ. AF Grey N.8 is a little lighter, cooler than RLM 65 (1938).

Can I use Russ. AF Grey N.8 instead of RLM 65 (1938)?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Russ. AF Grey N.8 is a little lighter, cooler than RLM 65 (1938).

Can I use RLM 65 (1938) instead of Russ. AF Grey N.8?

The same difference applies the other way round: RLM 65 (1938) is a little darker, warmer.

ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.