Ok I don't know anything about what to tell a cue maker on how to make the conversion, so I got a Brunswick Willie Hoppe and I want to turn it into a conversion. So what should I tell the cue maker what I want done to make it the best hitting cue it can possibly be. I don't care about looks.
You don't tell him how to make the cue hit well, that's what he'll do for you. What you can do is tell him some of the options that you want on the cue if you have any preferences. For example, wrap or wrapless, color of wrap, Hoppe ring or no, color of phenolic, fancy ringwork or plain and simple, joint type (stainless steel, ivory, phenolic, etc), pin type, etc. Pricing will be between $600 and $1500 depending on who does the work and exactly what you want done.
I would advise you to first call some of your candidate cue makers and talk to them about the options, get a price quote and an eta for completion. Your choice will then become clear. Good luck, and enjoy the ride.