Upping the flow rates past 19 for the 5.2 and 24-26 for the 5.9 will not gain power. Example:

My 1992 w250 5.2- Had rust in the fuel rails clogging the injectors every 3k miles. Can only get returnless style fuel rail from ma Mopar now so I switched fuel pump assemblys to use a 94 5.9 pump with a 2001 regulator and the black/blue 23 lb/hr 96-up injectors- BAD IDEA. Engine had flooded plugs at idle. Switched to the yellow 19 lb/hr injectors and much better but still chuggy at idle. I will have to go back to the 39 psi regulator. Getting 12.9 mpg in town. Pics here:
http://ramchargercentral.com/mopar-trucks/1999-w250-project/100/

On the flip side, in my 88 I am running a 2001 5.9 with red injectors at 50 psi and 1993 OEM electricals -is a beast- perfect throttle response, good top end all the way to the rev limiter despite the EGR style intake. And 14 mgp in town!

I think the maximum on a 5.9 is the 93-95 26 lb/hr injectors. But that was at 39 psi. You would need a turbo or supercharger to justify the 42 lb/hr and definitely a aftermarket fuel injection system like a MOtec

Again, I am convinced that tiny fuel line held these engines back when new. Look at a returnelss style fuel pressure regulator sometyime and see how small the hose is. I parted a 97 2500 last fall and the line was stainless steel, but looked like 1/4 inch from tank to the flexible part

Somehwere on the internet is a summary of Chrysler magnum injectors- its half right. THe injector years and generlaizations are wrong, but the flow rate math is right.