if the tune is right it will hold up!! we have put 250 to stock motors and 400 on mild motors with KB hypertectic pistons!! with the 75 - 100 you should be safe for a while. remember its all in the tune.:yes:
i have buddy running a Q-jet on a mud truck with a 150 hit on it and it works well. i personaly never ran a Q-jet with spray but have seen it done more than once. not sure if you would have to mod it or not. i know the mud truck carb is bone stock. as far as the plugs go i would run at least one step colder on the plug if your going to stay in the range your talking about. and to be on the safe side i would pull 2-4* of timing out and learn how to read a spark plug. on a N2O motor or any motor for that matter, the plug is everything. it will tell you if your too rich or lean and if you have the right amount of timing. there is alot to learn and i myself continue to learn more about nitrous and ive been running it for about 12 years now. take baby steps and ask if your not sure. good luck!