If you want to find out for sure what breed Mac is, there is a genetics test that can be done. Your vet would need to take a blood sample and send it to the lab, the panel is called a "Wisdom Panel". It's fairly new, but it gives you the breeds that compose your pup.
i dont know if anyone will read this but your puppy is absolutly my boy who just passed away like 4 days ago you should look at his picture. his mom was a purebred rot and his dad was a lab and he looked just like yours. but if they are the same be prepared. my boy was 120 lbs. when i lost him and he wasnt over weight for his size!