On the RR, the waterline on the southern shore is where Texas ends. If you're on water, it's Oklahoma. The exception is Texoma.
Best spot to drop in is just N of Gordonville.
If you're rollin an airboat posse, plan on getting a lot of attention from the GW's. If they give you sh1t about no fed duck stamp on your OK license pull up the regs online and show'em your fed stamp on your TX license is legal for OK. One stamp on your TX license is good nationwide per the FWS.
Seems like there's 50,000 OK GW's for every TX GW.