Underdrive crank pulley = more H.P. ?

This is kinda O.T. I'm trying to give my 145K mile 305 chevy
a little more grunt. Are the under drive crank pulleys you see in the Summit catalog the real deal or is the H.P. gain a dyno thing. Will I gain any real world power or are these things "snake oil"

Chuck Fish

 

World Products S/R 305 heads... They have 1.94" intakes and "Camel Hump" similar shaped ports.
I have them on my 262 and they love to make with the RPMs

Or just yank it out and put a 350 or 383 in it.

 

I'm trying to get as many miles out of the 305 as i can. At this point It's become kind of a challenge. I've used Mobil - 1 in it since new and it dosn't use any between changes. This is my daily driver not my hot rod. My hot rod has a flathead Ford in it ( a real motor ).

Chuck Fish

 

I think the pully might be good for a few hundredths of a second at the strip but you won't even notice it on the street.

 

if he does notice it, that would be the "alt" light glowing, and the ac blowing warm at idle....