This is something else missing from the pile of bits that will eventually become my '72 A65T

Apparently there are two types, the later type 70-8310 being the part that I need.
Apparently this later version is interchangeable with the earlier type - so what exactly is the difference please ?

And just to confuse things, there are some "funny looking" tensioners that have appeared on eBay lately.
The rubber pad is shorter than the original and stuck at the end oppersite the pivot hole.
Are these any use at all ?
Or are they just a part off a completely different vehicle (like a cam chain tensioner blade) that just happens to fit ?