No there are different sized ARB's @Drakec . Know this first hand because I ordered the wrong ones last month.
Get a vernier and measure yours, won't take two mins and it will save time in the long run.
I'm not sure buddy. I just measured mine at the inner bush as that's what I was replacing. Mine was the larger of the options and that's a non FF 182 if its any consolation to the OP.If you do measure it, i'd do it at the point where the bushes go as the inner and outer bush diameters are different aren't they?