Milling for compression

Warning: math is definitely not my strongest suit, even though I triple-checked it...

I just took a bunch of measurements in order to calculate the compression for the 225 slant (0.040" over) I'm rebuilding. I came up with the following, using krazykuda's formula:
The piston needs to be 0.050" below the deck for my goal of 9.5:1 compression on a naturally aspirated engine. It is currently 0.200" below the deck. That means milling a combined 0.150" off of the block and heads.

Does this sound right?
What should I do?
0.100" off the block and 0.050" off the head?

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Here are my numbers:
Cylinders are 0.040" over = 3.44" diameter
Stroke is 4.125"
Swept volume calculated at 628.36 cc
Piston top to deck ~ 0.200" = 30-31 cc
Head combustion chamber volume: 60 cc (averaged across 6 cylinders with block off plate, graduated cylinder, and patience)
Head gasket thickness = 0.040" = gasket volume = 6.3 cc
Fire ring = 3.5"
... Swept volume = 628.36 cc
... Clearance volume = 97.6 cc

These numbers yield stock compression of 7.5:1

How to Check Compression