OK, relatively new to the forum, so I don't know the lingo.
What's a "pony carb"?
some thoughts:
1) since your problem is with incline, my first instinct is that the new carb uses a side-to-side oriented float pivot/pin. As you go up a hil, the fuel moves back in the float bowl, the float moves and affects your mixture. A carb with a front-rear oriented float pin would have this tendency if you elevated one side of the car (driving along the side of a mountain, instead of up it)
2) mixture. If we're talking weber - the idle circuit is active until about 3000 rpm, after that the main jets kick in. At idle, to tell if you're running lean - loosely put your hand over the carb throat just for an instant. If you're lean, the RPM will go up significantly. If you're rich, it will die almost instantly. You can adjust the idle mixture with the adjusting screw. Using a gas analyzer is best, but I'm guessing you don't have one of those in your garage....
Main jets is a little trickier.