Green card experience letter format

Hi, Have a quick question about the green card experience letter format. Issue 1: I worked for Company A overseas and the Company name got changed to Company B due to a split that occured in its USA based parent company. Company C acquired Company B and they have all the payroll records of the Company B. How do I need to get the Green card experience letter format ? Issue 2 Company C (as specified above) is not willing to give the Experience letter in the old company's letter head. So, would my old experience letters suffice OR should i be pushing them to issue a letter for me? If Labor department validates my experienc, they would be still in the records but the issue is with obtaining the letter in the format Labor department is expecting. Any help is greatly apprecited! Thanks