Sportster in your picture seams to be fairly original except for the weld-on hardtail part of the frame. It has original front end with shaved lower legs and the builder has built the front wheel with a spool hub (no front brake

).
Basicly this would be an easy task to build from a original ironhead. But you say you have a chopper? Don't spoil it - choppers rule

. If you don't like it, sell it to someone who does and get yourself another project.
How about showing us a picture of this chopper in question? It would be a lot easier to tell you what to do if I saw what you have to work on.