For the gurus

Well If you go with leaf springs a 3 inch system will fit. There is a thread around here about that. Try a search for 3 inch exhaust and you should find it. The wheel wells on the Duster/Demon are wider than a Dart swinger so I think a 275 will fit with out mini tubing or relocating the springs. May be able to get away where there at or using the of set spring hanger kit. Will want no less than a 8 inch wheel for a 275. Sorry don't know about the off set.

As for if you use the street lynx kit. I don't know. LOL May try calling Bill at Reilly Motor Sports. He will be able to give you the down low on it.