Technical Sun Tach RA series?

So picked up this little gem at Turlock today. Figured a 4K tachometer would suit a mild flathead well and price was super cheap.

Well a little research and I’m able to find lots about the RC series but can’t find a thing about the RA. It has the early pinch bolt cup.

Anyone know anything about this series? It doesn’t identify what transmitter I need on the tag.

I also would like to know the date/age of it if possible.

Many thanks HAMBers!

 

I think that is for a Diesel engine.