I just made this recipe, almost exactly as you have presented it. I had never had corned beef from a can before but I looked for it and came up with the same one that you've described. I was skeptical to say the least. Even when I opened the can, I was immediately reminded of what we feed the cats in the morning
. There were only a few 'shreds' of meat in the can, and it seemed almost like a paste.
In spite of my trepidation, I carried on. My second area of (mild) concern was the use of sour cream in place of a thousand island or russian style salad dressing, which I have seen in other recipes for Reuben Casseroles (and an ingredient I always use when making traditional reuben sammiches).
Using your measurements, my 8 x 8 pan filled up pretty quickly... but I just kinda pressed it down and carried on...
To my surprise, the final product tasted better than I expected. The other flavors (sauerkraut, swiss cheese, rye 'croutons') kinda overwhelmed any flavor that the 'meat' might have had. And... as much as I like sour cream, I'll probably make this with some thousand island dressing (maybe 50:50 blend with the sour cream just to get the flavor in there). Additionally, I'll probably use deli sliced corned beef sliced thinly if for no other reason than aesthetics (but I suspect it would taste better, too).