i have an extra rz harness for sale
yes, you honestly only gain 5-10hp, my ported rz is making 56hp at 93mph, with stock head, very mild clean up port.
usable power is alot better too
the one on ebay is like 5000 bucks
i know someone selling an rzmotor and elec - condition inside unknown for like 600 bucks plus shipping, it runs but probably needs a rebuild
and you have to make adapter for pipes, and only a handful of pipes will fit it - including ROCKET pipes (email me, 425 bare, 525 triple chrome).
hope this helps!
its a fun project!