Not sure about Finn being a half and half. The facial hair smacks of a third breed - maybe father was a crossbred Bedlington fell terrier or Norfolk say. Check for the ear tips being turned out a rest. Tail carriage should be always behind the back and not over it.
Lurches also have collie crosses into them, so he could have some collie too. Do those ears prick up much when alert?
He’s handsome anyhow, and looks like he could get a gallop on.
Nib will run for miles, dig for hours, catch dinner and cuddle up with you on the chair.
Great thread this.