I know, nothing is close in North Dakota. I have a boy in the air force stationed in Minot and he tells me the same thing when it comes to finding a machine shop. So the question is, what is it that you are trying to do here? Rebuild a 248? If your goal is to rebuild a 248 then why mess around trying to determine for yourself whether you have a usable block, particularily if you lack the training and equipment to make such a determination. If could be a very expensive mistake on your part.
You want to know up front, without question, whether you have a block that is usable. And for that, you want someone who knows what they are doing to to give you that info. Mony spent investigating whether the block is a good canadate or not is money well spent. If you try this on your own, and make a mistake, miss a crack, whatever, then spend the money to clean and machine the block, only to find out you missed a big crack in a critical place, that is just a waste of time and money. So even if you have to drive a distance, find someone decent. Not just a machine shop that "might" do the work. Find one that "will" do the work, even if you have to strap the blocks to a pallet and ship them to someone.
So, if you really want to find out whether you have salvagable blocks, get them to a machine shop and have them do what is required to sort that out. That usually means a dip in the hot tank for an initial look at the cylinders and a visual inspection of the entire block. The machinist will run the dial bore guage down each cylinder and determine if the block has been previously bored out and if so, by how much, and if the cylinders are tapered from wear to the point they need an over bore, and if so, by how much. That initial inspection tells you a lot, like if the block will need sleaves or just a basic bore and hone. Now you have a real basis for making your decision whether to go any further with this block.
If the cylinders pass a manual inspection and are determined to be usable, and the block itself passes a visual inspection, the block next spends a bit of time in the shot blast machine, particularily if its really crusty, and they all are these days, lol. Once the outside and inside are nice and clean, magnaflux. If the block passes the crack test, now you have a real basis for rebuilding.
Just my opinion and yes, I know it costs a few dollars, but everything does these days. But you have not lived until you have spent all kinds of time and money on a rebuild, without doing a proper investigation, and then find out it has a fatal uncorrectable flaw, your heart sinks. Time, effort and money spent now will reap rewards down the line.
