184's with long nipps ... Custom Riders normally have a good stock 
How can you just come out with that with out even knowing what rims he is using , also ya never even said what cross ?
It will probs be best off as 3 cross and yes you may be able to use the 184mm spoke with the long nipples as the nipples will make up any length that you may lose if the spokes were to short .
If you what a job doing you need to do it right , you need to find out the ERD of the rim and the measurments of the hub then this spoke calculator will tell you , i always go for the nearest mm smaller than what it says so as to compencate for stretch on the spoke's ..
http://www.unicycle.uk.com/SpokeCalc.asp
