Jacuzzi's have a plastic wear ring.
If the boat has been started out of the water, once, it needs a new wear ring.

The impellers go from A to D.
The A is similar to Berkeley 2A,
Jac. B to a Berkeley  A, and so on.

The rattle could be three things,
The u-joints are worn out,
The spline yoke is worn out,
Or a stainless impeller has been known to rattle.

There is a stainless option in Jacuzzi impellers. Like finding hens teeth.

At over 500 hp, stainless is preferred. At 688 hp should be required.

It is a mixed flow pump, same as a Berkeley.

It already has the better shaft. Loaders would be a custom piece, as well as a ride plate and shoe.

The bowl and impeller could be changed over to a Berkeley set-up, as there are kits available.

Between the kit, and adding a ride plate and shoe to the WJ, a complete Berkeley pump set-up may be the best bang for your buck. All depends on where you want to go with this set-up, how fast, etc.

Tom @ Jet Boat Performance has the wear rings in stock. Also a plethora of information.

Jack @ MPD was the guru of WJ pumps. I don't know if he still works on pumps.

Hurry Round Hondo, a K (KJ) class 'jet boat', had a big blower motor, running a mostly stock WJ pump, was out racing and winning with the K boats. Until it was outlawed. This was in the early 70's.

And lot can be done with the WJ.
I have 2 of them (not for sale) and wouldn't think of replacing them with Berkeley pumps.

Btw, I also have a 74 Glencoe 19' jet. WJ pump. I'd like to see the rest of it.

Dan'l