It appears that there are alphanumerics on the BB shell below the NERVEX stamp. Your number found already could have a different significance depending on the brand. Have you measured the BB shell width and determined the BB threading? Also, do you know what the seat pin diameter is? I don't believe the bike to be earlier than the 70s, nor later than the early 80s given the top mount shift cable guide and chainstay cable stop braze-ons. Does the steerer tube have the Columbus ribs (5) or any external marks?Having cleaned back the bottom bracket and squinted at it in late afternoon light, I've been able to pick out a feint frame number, 11243, but nothing else definite. The numbers are round the RHS edge of the BB, rather than across. Any ideas, anyone? Could it be a date?