I have a feeling it would be a Good idea to put that motor back forward. I guess you can always try it this way first, then try it forward.... If its nothing but a wheeli machine you will want to put it up front for sure.
You will no right away. My personal experience is with Bogart's 1000cc team scream orange SJ. I think he said it was -2.5" and I could barely keep the nose down to turn for my setup! I didnt care for it much personally. He said a SXR would ride just the same if it were shortened as well...... I dont buy it! It would still be a much more stable platform IMO.
I may soon sell my round nose and start building a Kevlar/Fiberglass Trinity hull, and run a limited SXR motor. If I do, it will be -2" with extentions to bring it back to stock for surf riding.... But first I need to finish my fixed steer SJ project. Cant be without a boat.
Good luck!