What kind of exhausts do you have which they are specific for MC28 and you have these problems?
The JHA 500V2 type exhausts are specific for MC28 and they dont fit on MC21 without destroying from the swingarm the inside area of the right chamber.
Any chambers that fits also on MC21 are not specific for MC28.
On my MC28 the JHA 500 V2 type fits without modifications at the fairings or the mounts just bolt on and have a free space of about 1cm at every side of the lower fairings.
The only small modification that they need is 1cm spacers at the right footpeg if you use the stock MC28 as the chambers are designed for racing rearsets.
If you want i can take some photos for you tomorrow of these areas which you have problems to take a look how the JHA 500 V2 fits.
If anyone has any more infos for specific MC28 chambers i will also love to hear them.
I hope that i helped even a little.
Cheers
Stefanos