Try to adjust valve clearances with standard loose fitting tools then try Kent's tools!
All 6-cylinder gas engines during this period have adjustable valve clearances that should be checked every 12,000 miles. Only one wrench is needed to adjust these valves. There are no locking nuts like on the diesel engines. The 14mm or 17mm ball adjusting nut has threads designed to bind and hold it in place after you turn it.
1965 to 1972 M129 M130 6-Cylinder Valve Adjusting Wrench Set
$96.00
SKU:
GEG-M130VALVETOOLS 
Product Details
When using this tool you should have a long breaker bar at least 15 inches in length. A ratchet wrench would world but you will have to keep adjusted the ratcheting mechanism everytime you move it a different directions.
This is the 17-inch heavy duty bar we recommend. It can be purchased separately below.
