Can anyone help with installing downtube shifters?

I have a pair of NOS Suntour downtube shifters with the little plastic plugs (I realise these pull out to fit the shifters) that I'm trying to fit onto my Raleigh frame. However, they have a washer with a sort of tab and I'm dammed if I know which way up this should go on the bosses. Anyone done this before and can help with some simple fitting advice / instruction? Thanks.

Is the tab the stop that prevents the levers from going too far forward? If so, they should be mounted with the tab point up towards the head-tube.