Would putting a stock chevy 400 cam in a 305 make a difference?

The 400 cams were low-RPM, low-duration, low-lift stuff. Relied on the cubes rather than cam.

They were also all flat tappet. If your 305 is a '87-later passenger car, it would have come with a roller lifter cam.

If you are going to the trouble of changing cams, I would recommend an upgrade to a small aftermarket cam. Something around a 256 - 264 advertised duration. Just don't go to big or it will be a dog.

I'm not incredibly keen on SBC's, but isn't the 400 SBC externally balanced? I'm not sure if that makes any difference at all. I remember at buddy in HS trying to put a set of camel humps on his 400 and the ports or some crap gave him and I a ton of grief. I was amazed about how un-universal it was compared to other SBC's we had worked on.

External balance won't make a difference . All small blocks should be interchangeable. The only issue I can think of with 400 is that the heads require steam holes since the 400 has siamesed bores.