1. Ask you I140/485 lawyer
2. I think
a. If the old company will not revoke ur 140, you should be fine. coz GC is for future job
b. If H1B application form does not ask you such questions, you'd better not to tell CIS
c. If CIS does not ask emplyment letter, pay stub, W2 form, you are fine. Otherwise need your old company's help and need to send CIS I140 amendment.