The XB engines will bolt directly in, don't think I've ever seen an 1125 on an XB frame thougj. But the belt drive is different from 03 to the newer models. So you will also need an 04+ drive pulley, and sprocket/pulley for tje rear tire, and tensioner as well. This is a stronger belt to, you won't have to worry about snapping it as easy.
And as far as suspension, try google search, "buellxb.com,topic u want to search.com. I've seen the thread that your looking for, also. You could also check I.der general motorcycle chat/150+ helpful links. It might be in there. Good luck.