It's not "difficult to accept".
Nitrous oxide and nitro-methane are not the same substance, but for racing purposes nitro is an even stronger power adder (see Pro Mod rules).
My point is that you accidentally forgot to mention that tiny little detail (gasoline is not the fuel), as if it were of no consequence. My objection is that the conclusion you permitted to be drawn from your remark is (since all prior remarks dealt with pump gas) that a N/A GMC engine produced 700 hp on gas.
Anything over 350 would be quite remarkable.