PRC4606.
Only used for a short time. Mine (1986 'C' reg) has the same.
Problem they have is that the full current for the headlights is routed through the switch.
The contacts get hot & melt the plastic of the switch.
Because it melts the plastic it's not repairable.
Mine did 2 before I went the relay route.
They occasionally turn up on ebay but are eyewateringly expensive.
I don't know if ones with different plugs could be rewired to suit as I've never tried it.
I suspect PRC2956 MIGHT be worth a look & they are more sensibly priced.
If you have - or can find - a good one then your best option is to rewire so that the main, dip & flash operate relays.
The relays handle the main current with no problem & the load on the switch itself is hugely reduced.
DIY'd main using the info from an MGB forum - they use the same switch & had the same issues.
There are kits available& IIRC Boomslang was one of those.
www.paddockspares.com/pm330-boomslang-performance-headlight-loom.html
MGB forum stuff: