OK, your bike is a UK or European direct sales K2 by the numbers given
All K2 had a VIN starting with 20 until they run out of 20 vin numbers and the last ones manufactured in 1974 (registered 1975 in the UK and Europe) had VIN numbers starting with 21. The engine is a match for that year so, more than likely the correct unit.
You should have the later type forks fitted and still have the unicorn top yoke and K2 clocks. If you post some pictures of the handlebar switches, i will know more.
You will never be able to order a con rod via the engine number, these rods were matched to the crank by size and weight. Tell me the markings on the rod ? and i will be able to match it from one that i have in stock.
Another question : Why do you need a replacement rod ?