I'm gonna say 67 and here's why – a friend put me onto a similar
kit which I brought recently. I've researched it fairly extensively and came
up with this. Until 66 the drums have the older deco style lugs, they changed
to the 'pointy' style lugs in 67. By 68 there were further changes – drums
became international sizes, mahogany used instead of birch, tom mounts moved
to front of bass drum, spurs moved up to sit above bottom lugs (presumably to give more stability). My kit is pretty much the same as the one your looking at with the birch shells, mounts at the player side of the kick and spurs lower down.
A couple of things worth mentioning. These will be metric/pre-international size drums. Premier didn't make a 13" drum back then only 12" and 14" tom sizes. Most likely the toms are both 12". Some people a negative about the metric prems but heads are still available in both coated and clear ambassador and pinstripe models. Check out drumarchive.com click on Premier and have a look at the 66 and 68 catalogs.