1-In most cases you can't just dump more fuel into the engine to increase HP, along with bigger carbs you often have different heads, almost always larger exhaust ports....ignition systems
2-Your 9.9 Seahorse may be one of the few exceptions to above, only around 80/81 was the exhaust system larger/tuned etc. But its not the carbs that are different, its only the jets in the carbs-its same carb body. I think you just need to change reeds (petal plates) and carbs jets....everything else is ame on those engines I've heard.
3-Worries me that you think this could somehow increase HP
Search the net for details on rejetting your carbs, the guy who told me those 70's 9.9 Johnsons are are capable of being converted knows his stuff. You definetly will need Reed plates also, online they are half what dealers charge. Put Boysen reeds on my merc and it ran smoother, gained 200 revs.