Help about Employer LOR: (do they need to put a recipient address, use a letterhead etc.)

Karsa Orlong

An old boss of mine has agreed to provide me a LOR but was asking for some guidance on the finer points like:
- the recipient address
- should they use the letterhead from their personal company (I didn't work with them in this company, both of us worked for another company we no longer serve now)
- how long should the letter aim to be (page/word count)

Also if anyone has samples of strong LOR from an employer, I'd love to see them.

Thanks!