Spider wheels offsets - difference front & rear

[honcho]

Hi,

I know that the spider wheels are slightly different fron to rear - I understand that the rears have a built in spacer which pushes the rear ones out a bit further - could someone please confirm this and offer any information with regard to the relative wheel offsets - front vs. rear

Also if anyone knows where there is a set available (preferably used) then please also advise.

Many thanks