I have had 4 69 trucks they all had a sm420 with t221 tcase only trucks i seen with sm465 and a np205 tcase are 70 and newer or trucks that had been converted
One easy tell tail is sm420 front driveshafts is it has only 2 u joints
Where the sm465 setups have 3 u joints two make up a cardan joint
https://www.rockauto.com/en/catalog/...haft+seal,8416