You will need at least 70% of the rated HP to get satisfactory performance. If your boat is rated for 100-110HP then 75HP should be enough.
My guess is that a 19' cuddy would be rated for a lot more than 110HP. If so a 75 would seriously underpower her.
I had a 115 hp with 21" pitch prop on a similar size (but much lighter) boat and I enjoyed having a good fast ride at 3500 rpm instead of WOT. Food for thought ...Well I have a 1986 bayliner cuddy cabin 19' that I need to put a new motor on I am curious if 75 hp is enough, anyone have any ideas