ΔE 6.4, close: similar, with a visible difference side by side. Longbeard Grey is a little lighter, more muted than IJA #1 Hairyokushoku (Grey-Green).
Usually, if you are not matching paint already on the model. Close match (ΔE 6). Longbeard Grey is a little lighter, more muted than IJA #1 Hairyokushoku (Grey-Green).
The same difference applies the other way round: IJA #1 Hairyokushoku (Grey-Green) is a little darker, more saturated.
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.
See IJA #1 Hairyokushoku (Grey-Green) on the colour wheel See Longbeard Grey on the colour wheel
All matches: IJA #1 Hairyokushoku (Grey-Green) equivalents · Longbeard Grey equivalents