If the converter you will be using is a factory core, there will be a paper decal on it. On this decal is a code consisting of letters and numbers. This is how a GM lockup converter is properly identified, any other markings mean nothing. The code may say something like HB1, HZAD, CG3C or others. If you can get me that code, I can tell you what the factory rated stall was for the unit you have. GM used a 12" converter with the codes CB4C, CB5C, CF9C on their turbo units, and Corvettes(and all were lock-up style converters). Stall speed (factory rating) was rated on this unit 1800-2000 rpm. As I recall, there was NO particular converter that was used only in the GN.
With more torque, you will get a higher stall. You should keep in mind that GM'S were in those years low on horsepower and torque, and there was nothing heavy duty about the converters used in the TH200-4R or the 700-R4. Pretty basic units, with no brazing done the impeller(hub side), or the turbine. If you're looking at some good horsepower and torque out of your engine, I'd consider looking into a heavy duty converter from one of the aftermarket suppliers. Are you going to retain the lockup function of the transmission/converter?