thats the kinda motor i was thinking about but the one out of a truck 97 or 98 which ever i can find easier
IIRC the '96 and up vortec 350's were 255hp/330 tq, a long, long shot from 400.
I'm not calling out anyone in particular in this thread but you'll notice that all of the "guesses" are nice round numbers or numbers that came from a computer program. No dyno numbers to back them up. People have a tendency to grossly overestimate power numbers.
The newer motors (5.3/6.0) will make significantly more power than the vortec 5.7 will.
Regardless, seriously question why you want more power and what it's really worth. I got the horsepower bug when I was 18 and decided to build the 383 for (my then) daily driver. Spent plenty of coin doing it, full roller, vortec heads, yada yada.
After that, I saw all the things I really wanted from the truck (bigger axles, lower gears, doubler, fuel injection, etc) and realized I could've had all of them for the cost of the motor. I've never really needed the power in the rocks but I really did need all the others.
I have all that stuff now but what I'm saying is building the motor was the most frivolous and unnecessary thing I've done with the truck, should've been a much lower priority than it was.