I've got a 608, and I've measured the cylinder thickness too, and I measured the K frame .357 for comparison, I just don't remember what those numbers were. But I'll get back to you on that tomorrow, but I think the K frame was a tad bit thicker cylinder wall, maybe not though.
What I can tell you is the 608 is a beast to carry for self defense, I know I have done it a few times. The cylinder is extremely larger, and then add two more cartridges to it , a compensated barrel, and you have one very heavy wheel gun. The up side is, they shoot like a dream, even with the most stout full house magnum reloads.
My Son dropped a mule deer in his tracks with one shot from about 100 yds. with that 608. Hit him in the head and blew out the opposite side of his head. He was either shooting my 158 gr. Gold Dots or a 125 gr. XTP with a full H110 charge, I'll have to ask him tomorrow. No kidding, that mule deer just fell over and the legs / hooves went straight up, looked like a comic strip fall over dead caption.
GS