MrBasse, do you have access to a lathe? It looks like you could turn some hubs with similar dimensions that should be stronger. Just a thought. We're in a similar situation but went with turned hubs to work with some Northern Tools tires and rims. They should work with any rim that has a 2.75" x 4 bolt pattern. If you're interested I can email you our CAD files if that would help.
Team #3184
Blaze Robotics
Burnsville, MN