GenII D&R
I have one on a 01 gen II. This was Wong's template which are no longer available. Any of the Gen II RMK chassis have a longer chain case. One give away is the spec on the stock gearing. If it's in the range of 19/41 and has a 72 pitch chain then it's a longer case.
That said, when I did mne it moved down 2 and back 3. top shaft is through the tunnel. This mod required cutting away part of the right foot rest and trailing arm brace for the chain case. I simply made a brace that goes from the trailing arm brace up to the bulk head to reinforce that side. It may be stronger than stock.
I found it much easier to make this mod with the belly pan removed. This mod also uses a shorter belt. I used the XCR belt which is 12 inch centers if I recall correctly.