If the 5" riser set-up you're talking about is the straight style from an '03 or older bike, no, they won't bolt up. The older riser/clamp arrangment has rubber vibration dampeners. You'll need an older style top triple clamp or modify your existing top clamp. It's been done.
That's a good question. I don't recall seeing the '04 and up risers from a Custom model with a 3.3 tank. I have a 3.3 tank I was going to install while my 4.5 glln gets painted. I should know in the next day or two.
Well, I just measured the 3.3 glln. It requires 7.25" of clearance from the center of the front mounting hole. The factory 883C speedo mount's lowest point is pert-near 6".
Plan B.