engine power

[capecodmjs929]

I recently purchased a 18SF of 1975 vintage and love it except for the low transom, which some day when I am rich will get updated. I have a mid '90's mariner on it now, with the hope some day to upgrade to a 4-stroke for some obvious reasons when the engine is replaced too. Does anyone have a recommendation? Also, I am concerned with weight of the new engine too. I found the current one is 350lbs. Thanks all for your help in advance.