Getting worried-----

DR
If you are not concerned with getting the full potential from your combo, then a 9.5 Scr is a nice safe number.

Keep in mind that Scr is just a way of accomplishing the actual Dcr target. If you put that 256 cam in a 9.5 engine the Dcr will fall into the basement(I love saying that), and performance absolutely will not be optimum.It won't be that much slower though. The Wallace calculator puts the Dcr at 8.0 with 9.5 Scr.and that 256 cam with a 56* ICA. Since 8.5 would likely be the ceiling with iron heads, you are only 6% low.
Myself, I would be targeting that 8.5Dcr, which requires a 10.1Scr with an ICA of 56*.I am pretty confident that I could make it work with your chosen parts.
For example retarding that cam to straight up, puts the ICA at 60*, and would drop the Dcr to 8.3.Shazzam.
But again, since the chamber volume has not yet been determined, I think you are jumping the gun, in the worry department. As for me I'm kindof excited.
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Reading this over I noticed that bumping the Scr from 9.5 to 10.1 is .6 of a point. And that extra .6 point gets the Dcr up from 8.0 to 8.5, a .5 of a point.
But retarding the cam just 4*, drops the Dcr from 8.5 to 8.3, that's .2 of a point.
Seeing that in print, I would not hesitate to target 8.5Dcr. Not one second.
For the 90% of the time that you will not be running WOT, that extra .6Scr will be paying great dividends in; a)part throttle performance, b)fuel mileage, c)throttle tip-in, and most importantly,d)off-the-line,part-throttle pull.
Some of these attributes can be obtained with the 8.0 Dcr. It will just take more throttle to get. Of course fuel-mileage will be less with the lower Dcr, and cannot be recovered. And throttle tip-in will be a tad lazier. However, most of these would likely go unnoticed, cuz you would have nothing to compare them to.
Personally,I would target 10.1Scr with an .028 gasket. Then if I just couldn't keep it out of detonation, the .039 could solve it.The difference is only about 1.9cc; but it represents nearly 3% of the chamber volume.