BM 5625 Rocker shaft end stop

[Chris Matthew-Powell]

Hello,
On page 22 of the Spares Scheme catalogue, you will find this item at the top.
Do any members with late 3 or 4.5 engines use these?
I took down a 3 litre engine some years ago which didn't employ this component and I can't find any reference to it in Technical facts or my photocopy of a GA blue print of a 4.5 engine.
I assume you use two of these in numbers 1 and 4 rocker box and locate them with a little pin or shaft by drilling through the rocker box.
I am trying ( and failing spectacularly ) to build a 4.5 engine, and would like to get it right.
Is there any real risk of rocker shafts fidgeting endways without these? I've certainly never heard mention of such?