ADVICE:Baseline carb jetting/engine timing/spark plugs

18 initial/34 total should be a pretty safe starting point. That's what mine set at and it runs on 87 octane, so if you're running 91/93 fuel there should be some room to play around with it. Personally, I found very little gain running 93 n/a, even after adding timing and tweeking the fuel, so I just run 87 all the time to save a little money.

I run NGK FR6 (v power) plugs also. These are stock heat range for the later magnum engines. Personally I think that the NGK plugs are easier to read (timing, not fuel). For nitrous you may want to consider an FR7 or 8.

Run the carb you have for now. While I do agree there is something to gain with a larger carb, that doesn't mean it won't run well without it. Looks to me like it should do better than 12.50 in the 1/4 n/a.