Here is a graph of a real dyno test of a good used low compression stock 305 that had a set of
GM vortec heads + edelbrock supervic intake+ 750 holley+ comp XE262H-10 cam + headers
added. Now it makes 325HP. It still have a very low compression ratio.
Now remove the intake manifold and bolt on the Weiand 142 blower system kit for vortec heads.
Reuse the 750holley carb.
Now the engine will be supercharged. Reduce the spark advance to about 31-32deg BTDC
Now @ 6 to 7psi boost it will create easily an additional 100hp. Most likely more than 100hp gain.
That is 425++ hp all from a stock short block.
This particular stock block build up was WOT dyno tested over 40 times.
As long as detonation is avoided the supercharged version is under not much more actual stress when under boost. 7psi is nothing to a stock motor.
I believe the kit of the vortec heads retails for $2700
you do the math for yourself.