Spoke length

What's up guys. I'm not sure how to figure out what size spokes I'll need to get . I have a custom hub from cognito Moto for a gsxr in order to lace up a 40 spoke rim. Any advise on how to figure out my new spoke length?

It's easy enough, just drop the hub in the middle of the rim , measure out and take the average.
Most spokes get trimmed to length anyhow.
Who's lacing the wheel ?
I'd just take it to them and let them figure it out.
Any good wheel shop will have a large selection or make their own and if they don't i'd go elsewhere.

Sweet, I'll have to call around to some wheel shops. I called one shop and claimed they had nothing for a Kawasaki.

I found a shop that has all the specs on the hub I have, so that's great. They can make me a set if spokes for $130.

My next question is wheel size. I'd like to keep the 19 in rim in order to keep the geometry close..

81 Kz750h 05 gsxr1000 front end

I'm wondering what the pros and cons of going with a wider 2.5x19 rim would be?
Any advices ?

Cheers