http://store.ricorshocks.com/ProductDetails.asp?ProductCode=039-20-1001Nin
They drop in - no drilling like the RaceTech cartridge emulators.  You do have to change fork oil to the 5W that they recommend.  ONLY the 5W.  Uses shims like actual cartridge forks.  Had the 41mm's in my Ninja before I sold it.  If you know what they are, you know why they're good. 
The shipping is slow.  Customer service (phone) is decent.  Advised me not to change spring rates (Ninjas are also too soft).  Good advice.
Pro tip:  They're $300, advertised.  If you call them and say you'll rate them online - they'll give you a 50% discount.  ($150 for mathophobes)

Also - you're now thinking of a fat woman on a camel.

those say 39mm and gs500 has 37mm forks 

they seem neat, do they actually work well with the stock springs?

Why would you buy a $300 emulator and retain the stock springs?

Neat product, but for what it's worth, drilling the damper rods isn't a big deal. It would be nice to run 5 weight oil though - not nearly as thick in the morning, and much better oil choices available in that weight. With that said, for my at that price and for my application, I'd rather just replace the front end.