Vuini,
The crankshaft bearings are metric sizes of Ø30 x Ø62 x 21mm double row, self-aligning; and Ø30 x Ø62 x 13mm single row. Or that is what the original SKF bearing were that I took out of my 1928 F28 (1928 600EW). An SKF listing circa 1931 calls out a 20mm wide on the flywheel side with 1mm shim, and 12mm on the timing side. (The S6 uses a bronze bushing on the timing side.)
I cannot remember if the 600EW used Ø5/16 x 5/16 or Ø5/16 x 1/4 rollers for the conrod. I do have a broken E29 crankshaft that I could check, but I cannot find where I put it! Imperial sized rollers are difficult to get nowadays. I did buy a large supply (5,000) of Ø5/16 x 5/16 rollers many years ago, but did not replace the rollers in my F28 as the big ends felt fine. So don't know if they would require alteration. The S6 uses Ø5/16 x 3/8 rollers, so wider yet.
-Doug