[Super73]

Are we talking rwhp or flywheel-whp?

You did not mention what trans you have. Believe me, that will show a big difference in power from one to the next trans platform.

What wheels and tires, as that has a play in rwhp as well.

Stock for stock compared to the 317's, the 243's are simply a better head all around and will make more power exery where.
Smaller chamber = more compression
Better flow if both heads are in stock form

Back in 2002 I made 405rwhp with just a cam and headers in my 01 SS M6 car. That cam was medium sized by today's standards.

My truck however with ported heads, same ci, bigger cam and more compression barely made 410rwhp through a locked 4L80E. I eventually changed some things and got it to make 449rwhp and run 11.4x NA with an overly tight converter.