Difference between upright and slant? slants are 10000% more comfortable to sit at and play!
There were no GameKings before the 3802/3902 MPUs, so you can be assured it is either 3802/3902 (039 board) or maybe even an 044 board if its newer.
No, unfortunately, you cannot "add" slot games like Cops N Donuts or Money Storm to a GameKing game set. You either play the GameKing game set, and choose from the games it offers, OR you install the desired I-Game software set (like Cops N Donuts, Money Storm, etc).
Good luck and I hope you get it!