The bearings are multi-layered, starting with a steel backing, followed by a layer of copper, then Babbit, or other soft metal alloys, and finally a flash coat of pure tin to allow for quick wear-in of the bearing to the exact contour of the crankshaft journal. The tin flash coat is very thin, less than .0005". In most cases, the thickness of the steel backing is not increased on very big undersize bearings- - - -more soft metal is added. That makes for a tendency toward more wear or distortion of the soft stuff under heavy load conditions. Back when these engines were daily drivers, most shops wouldn't build an engine with bearings smaller than .030" undersize, and .020" under was preferred. If you don't plan to run heavy loads or do a lot of highway-speed driving, a deep undersize will probably work, but since the 235 and 261 engines share the same crankshaft, they aren't particularly hard to find. The less regrinding the better, IMHO.
The fine metal residue in the oil pan is what wore off the crankshaft. That's a massive amount of wear on the main journals for such a short-mileage engine!
Jerry
