You want to file the leading edges of both the impeller and the bowl.
Think airplane wing, not knife edge (weaker) while you're there, check the radial tolerances of the impeller to wear ring. It should be at ~0.0125" per side (radial), and .025" to .030" at the leading edge, if I remember right (shouldered). Shims will help you with your leading edge dimensions. Wear rings are available undersized based on your skirt dimensions.

Any questions, pm me.

Dan'l

21' Eliminator Day Cruiser
Mild built 454. 57 up river.
19' Saguaro open bow.
Vortec 350 sbc. 55, loaded with family, ready to roll.
19' Glencoe. 454, XE cam, Bassetts.
Best ever, solo, 71.8

Dan'l

450 HP should be quite obtainable with mostly stock parts.
Quite a few 460 builds here on the boards.
Impeller selection is key for the HP you want. Knowing what it already has helps too.

Dan'l

PMP makes pontoons out of Florida, and started in 2007. I don't think yours was made by the pontoons company.
There was a way to find out who had the manufacturers hin initials prior to the current owners. If that makes sense. I just couldn't find it.
The round transom hole for the jet bowl reminds me of a superjet. Who made the superjet, Hondo? Sanger? I can't remember.
Regardless, looks like a cool project. What are your plans? Big horsepower? Mild cruiser? Yard art?

Dan'l

I use the lightest spring in the secondaries, on a 750 Holley 4160.

Dan'l

With 425 HP, you should be around 5000 to 5100 rpm.

ADBA in Parker, AZ
March 31st, and April 1st and 2nd.
At Pirates Den Resort

Dan'l

Nice find!

Looks like a bankruptcy starter kit, complete with a blown Olds?

Good luck, and happy boating ahead!

Looks like it could be a circle race boat.

Dan'l

Race boat? Dry.
Family boat? Definitely wet, at least under way, and dry at idle.

Even wet headers throw some serious heat forward.

My old man cruisin' boat has logs and snails, just sayin'

Dan'l

I'd stay with a vacuum secondary carb. Pretty reliable and trouble free once setup correctly.
But I'm biased, both of mine have VS carbs, day cruiser and fishin' b?t?.

Dan'l

Thanks Brad!

Congrats on your new baby.

Slowly getting my junk ready for the river.

Dan'l

With the Panther pump, it will absorb whatever HP you throw at it. However, because it's an axial flow pump (prop in a tube) it hits a wall at around 5,000 rpm, (think big block) and more HP becomes virtually useless. A mixed flow pump would handle the HP better.

A tight pump is better for performance, and probably would be a better place to start. Plenty of tutorials on YouTube will give you an idea on how to.

After a fresh pump, I'd add HP with a cam and if needed some good flowing heads.

Dan'l

Any idea on what year or vintage the SBC has? Casting numbers on the block and heads would also help.
Impeller size? What pump for that matter too.

Comp cams and Edelbrock have some Dyno charts on their most popular cams, which, along with an impeller chart can get you in the right direction.

Just picking a cam with huge duration isn't going to be happy with stock (severely inadequate/smog) heads, but there are some factory offerings that are better than others.

I've ran as much as 235 degrees at .050 on a big block with logs and snails, with no reversion.

For a stock 350, the Eddy performer works pretty good, .420/.442 lift, and pretty tame.
Summit has a few inexpensive offerings, like the 1103, 1104, 1105, etc.

If it's a roller block, there might be a chance at decent compression, and Melling has a few rollers available and affordable.

While logs and snails and not the best for performance,  they're not nearly as bad as single exhaust on an 85 Camero or 85 Chevy pickup.

My short recipe -
96 suburban short block, stock roller cam.
Crappy but functional swirl port heads, 64cc (Compression ratio is 9.2-9.3 to 1)
Eddy performer rpm intake and 750 Holley, GM HEl. 1.6 roller tipped steel rockers.
Sprint car headers, with water added.
A Berkeley impeller.
55 mph at 4600 rpm, all day long.
Combo is 325-330 HP. It's not a rocket, but reliable as a brick.

Dan'l