anybody have any sugestions on what to replace the stock small round port heads with? I need to get new heads that flow a little better for a 96 mark5 454

Just changing heads?

I had the same problem 2 yrs ago. I swapped out the peanut port heads and the intake with a adaptor from quadrajet (manifold side)to holley.
I installed a set of stock L29 heads with only a valve job. I also installed a Holley 300-42 round port intake, no other changes and I picked up 10 mph (I did have to go up 2 prop sizes because of the xtra HP)
My boat is a Chapparal 2250SX with a Volvo Duo Prop
Before the change I could barely get to 42mph (gps) I am now right around 52. Well worth the effort and expense.
As a extra bonus, I get much better fuel economy, probably something having to do with the intake and heads having the same port size rather than the head having 25% smaller ports than the intake