As far as I know, there's only one manufacturer of reproduction deluxe horn rings. Personally, I would prefer original or NOS, get the C5ZA version for 65-66.
Google search for 'deluxe mustang wheel schematic' will help with assembly. The only trick is not over-tightening the spring screws. I've had to bend contact tabs to help dial in the horn ring to work at all 3 contacts on the wheel.