Your Jupiter SHOULD have a max hp rating of 85hp+/-, NEVER seen a 16ft Jupiter w/ a 40hp rating. Is it 16ft +/- long? Perhaps it's not a Jupiter. 40/50hp is typical on Jets and other SC 14-15ftr's.
If it's 16ft long, using the typical 75% of max hp 'rule' you ought to try & run at least 63.75hp, so you may be a little under powered, by 14hp.
Depending on the T&T on a 50hp, you might be able to swap the T&T to a 65hp Merc of the same vintage. If you don't max out the weight limit, I suspect you won't be totally disappointed w/ the 50hp, but you will probably want more hp eventually.