Ok just took measurement on my piston to deck and it is .145 and my CC of head is 55. Im taking it to the machine shop tomorrow. I going back with the same stock piston except .030 over.

How much do i need to take off to get 10.5:1 compression? Thanks all for the help!

ANYONE?!?!?!

As I mentioned in a previous post, if you replace the pistons, you must recheck the piston to deck clearance after you have mocked the short block up.
There are large variations in pistons compression height. When I punched the '63 engine from .030 to .060 over, it changed the piston to deck +0.020" on that particular build. They do this sometimes to keep compression the same as the bore increases. (The .060" overbore was further down the hole than the .030" overbore.)
Different aftermarket OEM replacements may spec differently. You must measure.

Have the machinist measure the compression height of your old pistons, and the new pistons prior to working through the calculations. Compression height is from the center of the pin to the crown of the piston. The measurement must be exact.

If your machinist has the capability, you should index the crank to make sure the throws are properly aligned as well. Original cranks tend to have rod throws that are not timed exactly. This issue can be exacerbated when the throws are ground. This generally won't be noticeable in anything but a large compression engine. At 10.5, your in the range to have detonation if something is off. If one throw is off by even a small amount, detonation can wipe that cylinder out.

CJ

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Part of Tyrde-Browne Racing

10.5 isn't bad as long as you have picked the proper cam to take care of the cylinder pressure(something like an Erson 280/270 is perfectly street able with this comp range and can give passable street performance).

Indexing would be good especially if you spun a bearing and are getting the crank reground

To keep your rebuild flow going in order, I would take a .090 cut off the block to get it in the ball park, then have it assembled, and then have the head milled to match the CC required to make your target SCR. Here I would use the calculator to double check the math before proceeding on the head (Note: This is YOUR homework assignment).

-D.Idiot