Give Claude Stanley at Freedom Sidecars LLC a call. His work is second to none. Just make sure you are sitting down when you get the estimate for the work and the time frame it'll take.
I had Claude build my rig an $800 Velorex 562 to a $3,800 DR650. After he cut, stretched, gusseted, plated the frame he located the mounts to the proper location on the frame. He then made a custom sub frame and cross spars along with a custom sway bar. Final cost was $4,000 and I opted out of powder coating and opted to save a few dollars by installing the tub and wiring myself.
A custom LL front end depending on the shocks and if the stock triples are re-worked or custom ones are made, I'd budget $3,000 to $6,000. Custom ain't cheap. Quality ain't cheap. An ill handling rig is no fun