Thank you Louis that is very good of you and likewise if you need anything I can check my spares box.
When Benjamin bought out Sheridan in 1977 they started using the Sheridan valve. Hopefully with my 342 being 1980 a Sheridan inlet will fit. I shall report back either way and If not I'll send Lawrie a message.
That does sound like fun having a dual shot pumper and without power restrictions where you are both shots will produce very good power.