Well, if you plan to use the stock '04-'05 XL-C clamp, forget it.
The clamp-light housing-speedo cup is a unit construction single unit.
You cannot just take the clamp, unless you are planning on buying one,
cutting off the speedo cup and then re-chromeing the piece.
But even then it will not look good since the speedo cup will leave a recess.
It is one solid chunk of cast aluminium that holdes both the lights and the speedo.
That yankee-enginuity clamp YE-B-03 looks nice
(did you check with them it will connect to the OEM connector found on the new bikes?)
but it will not give you the complete riser bulk look you mentioned.
The new XL-C riser/clamp unit is heavy and bulky.
It is different from the previous setup found on pre-'04 XL-C's in that it is not
just chromed tin covering slim risers, but a unit construction, billet-style chunk of chromed aluminium.
Oh, and another drawback is the riser block will NOT fit with standard top clamps, as the bolt pattern is different.