Is this correct?

[bushwesl]

+2 A-Arms w/ 3:2 offset = +3 A-Arms w/ 4:1 offset

[honda380]

looks to be right.

[250Renvy]

I don't think it's as simple as that.

Depends what rims you have and what A-arms. Not all A-arms are precisely +2 or +3. Not all rims are true 3-2 offset or 4-1 offset.