An aftermarket Taiwan XS1B shock, original 1970-1971 shocks (with blue spray-paint), and original 1972-1973 shocks.

First, let's dispense with the Taiwan aftermarket shocks.
Here's the current cheapest link:
https://www.ebay.com/itm/152151308883
or:
http://www.nichecycle.com/ncs/categories/suspension/shocks/17-06710-xs1b-shocks-by-ncs.html
Currently about $74 total shipped to your door.
They are junk. Very cheap components. They aren't even engineered correctly. With the bottom adjuster set at the stiffest (highest) setting, the bottom shroud will get crushed after the damper compresses about half-way, and/or damper travel will be impeded.
They are very pretty shocks. They're only usefulness, in my opinion, is to put on a bike that you are intending to sell. Let the new owner deal with the poor performance. If you intend to use a pair for yourself, I would at least cut the bottom shroud down so that you don't risk the crushing issue and restore full damper travel.
The Taiwan shock is significantly less robust than stock, and has less damper travel. The spring (previous pic) is also a lot cheesier than stock.

The stock and the aftermarket shrouds are the same outside diameter. So, if your stock 1970-1971 shrouds are poor, the Taiwan shrouds can be made to work, with a little modification. First, you will want to cut down the chrome lower shroud as previously pointed out.

The shaft hole in the Taiwan shroud is smaller than stock, so it will need to be enlarged. Also, note that there is no inner lip (arrow) on the aftermarket shroud. That lip strengthens the stock shroud, and keeps the spring centered. Another example of the aftermarket shock's jankiness.

Aftermarket (left and stock top eyes, showing why the hole diameters in the previous pic are different. Note that the stock eye is more robust.

The shaft hole in the Taiwan bottom shroud is a lot bigger than it needs to be, and once again, does not have the strengthening inner lip that will keep the spring centered...

...resulting in a very sloppy fit.

So really, what were you expecting for $70? The aftermarket XS1B shock has been cobbled together from existing cheap shock parts. And a pretty candy orange shroud has been added. If you search through eBay or AliExpress, you will find several examples of $70 shocks using the same components. Intended for bikes in the 125 to 250cc range. The example above, is even "Hign" Quality!
More to come, including a look at the 1970-1971 stock shrouded shocks compared to the 1972-1973 unshrouded shocks.