Agree with lab/bully breed mix of some sort, maybe some shepherd in there. Basenji is a definite no from me - the only thing I see in common is the prick ears, and that can come from a lot of dogs. I could be wrong, but they're an uncommon breed to begin with, so without an extremely strong physical resemblance I'm doubtful.
Lots of dogs have tongue spots, by the way! Including purebred labs, German Shepherds, etc. so pigment on the tongue is not a 100% proof of chow heritage. I'm also uncertain about Dane - how big is he? He does seem heavy boned, but Danes are cropped to have pointy ears, they're naturally floppy. Plenty of labs in the US are bred to be quite large - not necessarily the ones you see used for hunting or in dog shows, but a lot of the irresponsibly bred pet lines who'd be likely to contribute to a mix can be quite big dogs! When I was a teenager there was one in our neighborhood who easily broke 100lbs without being excessively fat (I don't remember if he was fatter than he should be - I wasn't very dog-savvy at the time - but he wasn't an obese butterball by any means).
