Unless you have a special reason for wanting to get an MT precision test bar I suggest all you need to do is spelt out on John Moran's web site
This is a good place to make a start on checking out your machine and I think helps explain the high cost / rare as hens teeth availability and price of these test bars. Most people would use the methon or a derivation based on John's web site description as they would have the necessary dial test indicator as part of their basic tool kit.
The only use I can see for these test bars is for rapid repeat setting and associated resetting of the compound slide after turning short tapers. Even then there are other methods of achieving the same result. Checking the MT in the head stock for concentricity with the bearings and alignment on axis is another possible use but as there are no adjustments to correct this other than remaking the Morse Taper I don't see the need for such a test bar unless you are in a production environment and there are other / better ways of achieving the required accuracy to a better order than using a test bar.
Hope this helps - regards Pat