Cali may only fish lakes restricted to 10hp, the game wardens may check serial /model#'s. That being said $700 is way too much money, and he would be way ahead trading up. If however he could pickup the parts used at a reasonable price and could do the job himself, the modifications may be worth it. I picked up a new late model head{larger intake tract} with all the goodies, and a used 20/25hp carb for my 18hp on ebay, rebuilt the carb,bought new gaskets and installed it . I don't have any idea on the amount of hp , but I gained a couple mph on a loaded boat and spent less than $100. I enjoyed doing it and earned some bragging rights too.