Mine were actually two different brands of pots but electricity doesn't know that. I stuck a meter on them and they were nearly identical in resistance. I have the pots to upgrade the stock pots right now but I am not interested. Your Gibby P90 have a PAF DCR of around 8.1ko.While I had the guts out I looked at the pots and caps but I didn't change them. I had Epi P90s in my Casino which I upgraded because they had a DCR of 12ko.
The GC Jr Casino comes with Gibson P90s so you really have nothing to upgrade.