@Jerry.Atrick , maybe this Wikipedia article will help. It’s certainly a lot more to design than the universal joint design but the idea is to suspend the platform on parallel links - where they cross is the point at which the whole platform will rotate - but that point will move as it tilts, too - depending on the length of the arms, etc. No such thing as a free lunch! Try the free program Linkages so you can play with it.
But, if you’re ready to start welding and don’t mind this version being “1.0”, I say go forward with what you have. You can always learn from it for the next revision. There may be other things you want to optimize in a second version or maybe 1.0 will suit you fine