If you can hear the engine screaming and it's sounds like it's maxed out with a 13x16 on it, you either have a really, really powerful engine or your "ear tach" is way off or it isn't really a 13x16. 

13x16 is too much prop on your boat and is most likely keeping RPM's down and lugging the engine  I'd probably re read the markings on the prop to verify it's diameter and pitch

13x13 would be a better prop, it'll give more RPM's at any given speed, lug the engine less and should be plenty of prop for a 318 to handle without over reving

But....... without an accurate tach, it's hard for you to know what you're doing.

Do you have one of those fancy timing lights that also has a tach feature built in?

How about a picture of those markings?

Shaft spinning easy can be good or bad.  Good if it means dead-on alignment but maybe not so good if you have too much wear in the cutlass bearing.

Glad you figured out what you have for a prop.  I will say that once a prop is reconditioned in my experience it doesn't spec out quite the same as when it was new.  In other words you might not be able to say "13x15 gives me x for performance" since a brand new version of the same prop would give different results assuming there were some minor changes during the recondition.

There's a lot to matching props to boats to engines, but then again you've got an old school inboard with an engine that, if close to stock, puts out a pretty well known amount of power.  Once you can trust your tach you'll be looking at speed vs. rpm and deciding if the current prop, and then the 13x13, are letting the engine make full power throughout the range.  Don't change out the prop until you get the tach so you have reliable numbers to compare, your gps max speed is one part but you need matching rpm to know what is going on.

And not likely to hit 50 mph with a stock 318, but 44-46 feels pretty fast in these boats!

I'm not able to see the pictures from earlier in the thread, not sure if that's on my end or they are gone.  If you are able to re-post or add some pictures I'd love to see the boat.

Umm...........Google says it's about 3018 miles 

Send the pictures

Here are Daryn's pictures mostly oriented the right way 

Glad you are finding stringers to be in decent shape.  Boat looks great by the way.  Now to really challenge you get a video or 2 of it running on the water up on Youtube and link them here.

Not sure I would have put foam back in.  I don't know how people feel about foam as a safety item, for me if my '63 (never had foam) sinks, it sinks.  One time in really rough water on a lake I shouldn't have been out on, I tied a lifejacket and inflated fender to my anchor line and the other end to the boat so if it sunk I'd have a chance to find it again later.  Not sure I'm proud of that one, but it was an adventure. My point is having a bilge that is dry and can be cleaned up seems better to me than having foam, but maybe I'm wrong about that, not sure.

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