I needed to compression test my John Deere 955 tractor but my compression kit only had ones that thread into the injector hole. The 955 uses a Yanmar 3TN84RJ which doesn’t have any threads on the injector. It relies on a metal bracket that goes over top and is bolted down. 
This adapter that takes one of the other threaded injector testers and allowed me to check the compression on my engine. 100, 43, 100. So it went to be rebuilt.

The blue rings in the picture are tpu gaskets. You might be able to use o-rings. Or it would probably work without any gaskets.