The 248 with flat pistons was a very short production engine. They were used in 54 and 55 and then discontinued. Finding any kind of pistons for a 248 is going to be a challenge. I could cut my losses and find a 270 or 302 block for which parts are available or find 248 with pistons in it that will work with just honing the cylinders. I am 77 years old and we had GMC's in our business when they were still current production. Installing salvage liners like Jerry suggests will make your engine like new. But even standard pistons are hard to find. We installed salvage liners almost 60 years ago, but if more than one cylinder needed one, be bought a new short block because they were still available then. Even if you find .060 pistons I would have the cylinder walls sonic tested. I would never bore an almost 70 year old engine .060 becaue you don't know how much corrosion you have from the water jacket. Salvage liners like Jerry suggests would fix this.
