Over tightening the disc can affect its release pressure. I can see it being a particular problem if you use a washer that is stiffer than the intended plastic one. It could easily damage the disc (or the base of the cup).
In the Sherwood manual it says to torque the burst disc to 50 – 60 in*lbs
I would get the 2015 psi ones (Sherwood P/N 4000-940), but Bryan may be able to special order the 1800 psi type (Sherwood P/N 4000-970).
The new burst disc plugs are far superior to the single outlet plugs.
The single outlet plug (even without the lead plug) will shoot the air in one direction creating a single jet nozzle. If the burst disc lets go, it can tip over a standing tanks or make a tank that is laying down tumble out of control.
The jet is small enough that the tank can be held, but if it starts tumbling around it can cause some damage.
Note: I saw a number of burst discs let go when I worked at DSC (in PR) back in the 70’s. What I hated the most was when the burst disc let go while filing the tank inside the water bath. There was no way out of getting totally soaked.
At least our water tank restrained the cylinder from moving around too much since it was a narrow and heavy aluminum container.
Now-days, the plugs are always supplied with the burst disc and they are supposed to be replaced together as a pair. The plug is the cutter for the discs. If they are not replaced as a match pair, it was found that the release pressure became less predictable. Which could in part, explain some of the premature burst disc releases we used to experience. I am sure corrosion in the Caribbean was another factor.
The new plugs have three outlets to balance the thrust from the gas flow and (more important) they will capture the pieces from the ruptured disc to avoid injury.
AFAIK, the old style plugs are required to be replaced with the new style according to the CGA (Compress Gas Association) codes (for all the reasons mentioned above), but I don’t have copies of the particular CGA document that referred to this subject. CGA documents are very expensive and I only have a few.
In practical terms, there is no one enforcing the valve burst disc requirements (unless you have a knowledgeable LDS) so the CGA code is not as big of deal, as for example the hydro requirements. But, there are other good reasons to follow the codes.
Here is page from the Sherwood valve manual that may be usefull: