Do you like Gitz trolls or are you interested mainly in the Grots?
If you like the trolls, they would be usable for both factions (I even remember seeing a troll gitz list using kruleboyz trolls even getting good results in a tournament recently). A Breakaboss and a Marshacrawla would be good buys for this route.
I can't help much with Gitz in general, but for the Kruleboyz part I can't recommend enough the Snatchaboss on Sludgeraker. He buff is really strong, helps your whole army, is good by himself and is a awesome models (IMO). A couple more boltboyz go in most list as well. You don't need more gutrippaz if you are ok with spaming the boltboyz, but if you don't like this route a extra unit of gutrippaz to round your minimum battleline is a good next buy as well.