Are the rearsets interchangeable between MC21/MC28 and even MC18?

I am trying to buy some aftermarket racing rearsets for my MC28 (or SP rearsets) and I would like to know if I have to get model-specific rearsets (or back steps as they're called here) or if I can get some that are off an MC21, etc..

Also will the position be different if you fit the same rearsets on different models ...

I'm looking at these for example:
http://page3.auctions.yahoo.co.jp/jp/auction/c68903538
http://page11.auctions.yahoo.co.jp/jp/auction/n6552652

Why do I need new rearsets? ... story to follow
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MC28 SE -sold-
MC21 with RS250 engine -for sale-
MC21 race bike -soon for sale-

21 & 28 steps are interchangeable, however the 21 steps are further back than the 28. The 18 steps fit the 18 only

Thanks Matt,

somebody told me that the brake master cylinder mounting bolts are a different distance apart. I am guessing that that is the difference between 18 and 21/28.

P.s. Thanks for the front fork adjusters, they arrived in good condition, and now my suspension is much improved.
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MC28 SE -sold-
MC21 with RS250 engine -for sale-
MC21 race bike -soon for sale-