Chances are that you may not able to use that LC approval notice unless you are working for that company again.
If your current W2 earning is more than the salary required on LC, and the small company can help you to sponsor for the I-140 application, and it had some profit which is more than your salary, you still have good chances to have your I-140 approved (given your friend can still ehlp you to provide any help).
When you submit your I-485 application, you need to attach your W2 form, technically they may find out you were not working for the same company in the past. It is still uncertain for your case to get I-485 approved.
But it worthing trying with this opportunity.
In the mean time, you should file your PERM as soon as possible. A pending case is better than any watching, you will lose a lot of time if you can file the case but you didn't, USCIS at least tried to process the cases in a "first come, first process" manner.