Great Question!
Parkers make EXCELLENT diving platforms, and it's the primary reason I own one. Since you are an experiend Parker owner you already know about the huge cockpit, and stability of the low deadrise design. Because the freeboard is moderate, entry and exit is a lot easier than on most vessels.
As for modifications, I have several major and many minor that make our diving more enjoyable. I have fabricated horizontal tank holders that are mounted beneath each gunwale and set off the deck on oak saddles. Tanks are out of the way and secure.
I have also modified a rod-holder in Stb gunwale to hold our hand-spears. I ran PVC tubing under the gunwale to the deck (over the rod holder diameter) to keep the spears from moving around and boinking toes. You can see it in the stb aft gunwale holding spears below.
(Don't forget the Boat Dog. They make excellent spotters)
Mounting the dockbox that you see the divers sitting on above was covered in this project :
Dockbox Mounting Project
I added a 3-D chartplotter to give me better "eyes" on potential dive spots to avoid wasting time on not-so interesting bottoms.
Here is a link to the 3D Chartplotter project:
3D Chartplotter Project
As for ladders, we just use the OEM swim platform with a rope stirrup to extend below the folding ladder. We have a notch-transom Parker so we don't have a bracket. I suppose the bracket would make a great swim platform, but I don't have any experience with that.
Every dive team develops their own little tricks and routines over time that make the diving easier and more fun. You'll come up with lots of your own I'm sure. You can bet the fact that you own a Parker will be in your favor!
Have fun and be safe!
John