40 to 50 years ago, it was unheard of to open a 50s GM 6 and find no ridge. Now it is quite common. My theory about this is that the last ring job saw very little service before it was parked. Possibly the previous ring job used chrome rings that never seated or whatever. By the time the vehicle was reaching the end of its duty cycle, people cut the ridge to get the pistons out without breaking the lands, broke the glaze, and threw in a set of rings.
I have used a variation of enginenut's method. I use a 10 over ring filed to fit at the bottom of the hole and then take measurements on the way up. I have a bore gauge, but the ring method is just as good on an old engine. Very few engines were bored in the vehicle and most oversizes were done by one of the 100s of machine shops that rebuilt short and long blocks in those days. Even Sears sold rebuilts.
I have played with a lot of Y-blocks, and have 4 56 Fords with Ys. They are very hard blocks compared to the GM. I am not familiar with Hudson, but Chrysler flathead blocks were even harder than the Ys.
Chances are pretty good that if you are willing to do some hard work, you may be able to hone the 216 to where it is servicable. But it takes a good hone that puts pressure on the cylinder, straight stones, lots of honing oil and lotsa work.
