Magnum head swap compression increase

I'm not looking for exact numbers, just a general idea. This is low buck stuff here.

I already have a few sets of magnum heads. And an intake. I'm not bringing the heads to the machine shop, or the short block. I'm taking a free short block and bolting free magnum heads on it.

I have searched for this answer and all I read are eq this or machine shop that.. stuff I know but don't want to do right now.

Anyway, ABOUT how much compression can I expect from removing the open chamber heads on my mid 70's two barrel 360 and putting on some stock magnum heads?

Thanks.