For a Sub/SD of this era, your crown options are the 7mm Twinlock, or the 7mm Triplocks; to further clarify, there are two different flavors of Triplock- vintage from the late 60's - 70's and then the current modern crowns.
Since I like pictures, here is one to illustrate the Twinlock:
Here is an early Triplock with cheese...
And of course, modern Triplock...
Note the differences in coronet on the Triplocks....
The modern Triplocks are the easiest to find... The vintage Triplocks and Twinlocks pop up from time to time, but are usually a fair bit more expensive, and not quite as frequently found. In addition, the Twinlock requires a specific tube, as the threads in the Twinlock go right to the opening (whereas the Triplocks start halfway inside and go up to clear the external tube gasket).
Hope this helps...
Best,
R