porting 587 heads....

Don't mean to hijack the post. But it is kinda related!

Has anyone machined the spring seats on specifically 308 of 576 heads to get additional installed spring height? If so, how much.

I realize core shift may affect the thickness a bit and the castings may be too different from the earlier heads to use them as a reference. But I'm trying to find how much or how little material is there.