These 'AS' cases are shown in the factory ledgers as spare engines for military contracts. Most WD contracts had around 10% spare engines.
Based on some fairly close numbers in the incomplete surviving books, I suspect this may have been an RAF spare engine assembled around November 1940.
It would probably have carried a small brass plate stating "Cat. No. 3787" (The spare part number for a complete engine unit). I would certainly expect two small screw holes close to the number stamping.
That's a difficult question. What's a good set ? Do you have the rest of the parts ? Do you mind the spare part case number ? Does it have a (matched) timing cover ?
Reasonable complete engines seem to be around £250 and should have plenty of usable parts.
If they're really NOS and have absolutely no damage or wear on the lugs (the biggest problem on used cases) then I'd guess £100 - £150 because they would form the basis of a good sound motor. If they're a bit scruffy and need any welding work then £50 - £75....but it's guesswork on my part.
You can still find knocked about cases for £25 at UK jumbles