I just installed a unity S-6 on my 50

Not sure if its one of the safety lights used but it looks just like the one in the accessory Manual

There is a Appleton spot light in the for sale section.

Just make sure whatever you get has all the brackets, outside and inside.

You'll have to drill a 1/2 hole in your A pillar
Luckily for me the hole was already in my truck.

I like the look of them on the AD trucks

I have a pic of my Dad driving an AD flat bed in ...1956...
No spot light, but it did have a visor and the turn signal on the back of the cab. so I bet the old work trucks did get the accessory s needed.

Good luck