Anybody ever do anything to these motors to get more power out of them?

Turn it into a HP500 pretty simple.

What needs to be done?

I was kind of kidding. I would slap a small blower on it like a 250. The 425hp motor is pretty stout and you would spend a ton of money getting it to 500. You would have to take it out to a 496 use alu. heads an edelbrock air gap and a good 850 holley. That a lot of money tied up for the gain. Slap a blower on there from the classified section and you are there easily and pretty reliably.

What is your application? Are you running the motors now?
I run a pair of them in a 29 formula, with impco aluminum exhaust, stock merc ignition, a dual feed holly carb size ?50 or850 , stock merc aluminum intake with the brass crossovers.
Carter electric fuel pumps and the stock cams that come with the crate motors. Turn key dependable. RPM's max out at 5000 top speed I'm not sure of, I just tossed some new props but my gps speed o internal antenna battery died.
You can get considerablly more out of the motors depending on how large your wallet is.
Grumpy jenkins heads, wild cams, huge intake, bigger carb, mallory ignition, bigger fuel lines, roller rockers, and then you have to get everything to come together and hopefully be dependable. And after all this what is your outdrive? TRS? Bravo1? The TRS Hangs pretty deep in the water and there is a considerable loss speed due to that?????? Sometimes staying fairly stock is a smarter move, unless your passion is big motors and big horse power, and hopefully your ritch!

Would a 250 blower work well on this motor with its 8.75:1 compression?

Yes they are running now. I have number III drives, with 26p props. I am only able to turn them to around 4200 rpm's. I also have gil dry exhaust to the tip.

Someone?

Call the people that sell the blowers.
They want to stand behing their product, so they must have a basic requirement of a base engine.
Ask them what it is.
They may not like your compression ratio or your camshaft, they are the only guys who know the details.
The blowers are engineered for specific applications.
Good luck let us know what you find out.

Yes a 177 or 250 would bolt right on. 5lbs boost would be very safe on the forged factory internals and would wake it right up!

How much hp would I get with a 250 and 5lbs of boost?