WhenI left school, our tractor was an Australian Chamberlain, 2 cyl, horizontally opposed, so an even exhaust note.

Neighbour had a JD 830, twin cylinder side by side, exhaust note the unique whump,whump,miss,miss.

60 years down the track, the sound of a Chamberlain horizontally opposed engine makes the hair stand up on my neck!  I worked mine for 8 or nine years,