Joe - Thank you so much for the reply. I will try the MBR2GPT utility and let you know how that goes. As for the NIC driver, yes, that is one of the ones we have tried.
I have also recently stumbled upon this article, which says that newer Dell systems are simply incapable of booting an internal disk drive through Legacy boot: Newer Dell systems unable to boot to internal boot device in Legacy boot mode | Dell US