I started working for a dealer in the fall of 1960. The items you mentione (except the belt pulley) we changed a lot. Customers wanted different front ends, different brands &amp; sizes of tires power steering or no power steering, etc. You swaped the items with the tractors you had on the lot. Once the 1600 &amp; 1800 models were the normal tractors we were about out of the swaping business except for  tires &amp; wheels. We were then out of the 770 business although the last 770 we sold we had to add a belt pulley as a front mounted pulley was no longer available from the factory.