For what it's worth illustrated options are below.
First picture shows (from left to right)
* An Apeks 1st stage with a clipped disk (piston) from ISC for a COPIS Meg.
* In the center is a blanking plug from TecMe with an o-ring on the perimeter.
* A brand new Apeks 1st stage with the uncliped disk.
The second picture shows the two sealing options.
* The clipped disk the built in diaphram seal is re-used.
* The TecMe blanking plug utilizing the o-ring. No additional sealing is needed and the plug has a flange to compensate for removing the diaphram.
Sorry for the huge pictures.
Thom
.