How much can I mill off the block

I have a case SC 1952 the block surface was pretty beat up the previous owner. I also have two cracks in the block that extended through the top of the block and down the full length of the stiffeners between the cylinders.Because welding cast is not an option in this area I have repaired them the best I could by installing a piece of 0.90 304 stainless double this is the thickest and strongest material I could find and install in the limited space that I had,and still have room for the heads of a grade 8 hex head bolts to clear the sleeves. However There was No room on the other side to install a nut so I tapped the attachment holes for the repair in the block casting stiffeners and installed the repair straps. My question now is how much can I safely remove from the surface of the block? I measured the height of the pistons to the top surface of the block at 0.29. I intend to seal the repair and the crack from the inside of the block with 8802-B2 aircraft tank sealant it has a temperature range from -65°F (-54°C) to 250°F (121°C), I have seen this stuff on 30 year old aircraft still looking like the day it was installed. Thanks for any help or comments
Byron

Having a hard time following all the stuff you mentioned in you post, but if you mill off the top of the block you are going to increase sleeve flange protrusion by the same amount and when you torque the head down with excessive sleeve protrusion you will likely crack a sleeve or the block counter bore if you don't also cut down the counter bore for the sleeves. I can't see the top of your block from here, but the head gasket does all the combustion sealing at the sleeve flange, and the rest of the gasket seals water and oil passages and a modern layered gasket will probably handle some varients/gouges in the block surface, without milling.
Loren

Loren is right. If you take 0.004" off of the head, then you will also need to remove about 0.004" from the step in the bore at the top of the block. Otherwise your sleeves will stick up too much. The sleeves must protrude 0.001-0.004" so that the cylinders and all of the other passages will seal properly. You will also need to make sure that the bottoms of the sleeves won't run into anything at the bottom of the engine (firstly the block casting, but also the rotating crankshaft and the rods) when they are installed at the new depth. Other than this, you only need to worry about increasing the compression ratio, and making the top deck of the block too thin. I wouldn't hesitate to take 0.010-0.015" off of the top of the block. But, you will need to be prepared to pay a good machine shop $50-$100/hour to do the work. Remember, there is a reason that they call it "Boring." Also, while boring a round part with a lathe takes time, boring a block with a mill takes more time.

Byron, I have a good extra block? Dick

I think I would do as Dick said and find another block. By the time you are done decking and cutting the counterbores you are going to have more into it than a good used UNCRACKED block would cost.
If you are set on saving your block and don't want to cut the counterbores the sleeves could be shortened to maintain the right standup. This requires accurate measuring.

Thanks for all the response's folks, I had no idea milling the counter bores in the block would be so expensive. I called a few places yesterday in Tucson the ones that could or would do it must have thought I was talking about working on an aircraft utterly insane prices. I'm posting the pictures of the block and the two repairs I was talking about. The top of the block is out of true by .015 but I'm thinking now that all the work was for not. I may be looking for a good block unless there's something I'm missing here. I'm in Willcox Arizona my emails open Thanks Byron

My Email should be open if not look on modern
Thanks again Byron