Engine doesn't sound too bad to be honest. I wouldnt be surprised if that 'knocking' noise was the exhaust blowing somewhere around the manifold, or the carb hitting the bulkhead. It didn't look like he had a box section for the weber.
What cam has it got? That might explain the rather lumpy tickover.
If you're reuilding it anyway i doubt you'd have too much to worry about. Have you thought of the sort spec you want?
i really hope youre right mate. ive got no idea what cam its got, i assume its standard or he would have mentioned it in the listing. ill probably give it a good clean up and a lick of paint and then drop it in so i can fire it up then go from there, if it sounds dodgy then ill pull it out and give it a rebuild.
the spec wont be anything toooooo mental if i do rebuild it, all depends on budget, but might stick a tasty cam in and maybe lightened flywheel or something