[cas3]

Does your 41 have two tail lights? If so, a period correct turn signal switch can be installed with a few changes, your front marker lights too can be blinkers if you have some skills in that area. I rarely drive on urban freeways, but when I do, I pay attention to whats around me, and make the lane change with no signal.
I do this in my modern car too, Why? If there is room to move, and you are traveling at the same speed as the cars around you, just do it....its called merging. Law says, no signal required for...I forget, 500', or 1000', but again, if you can do it safely, just do it!
A flat tire and you are trying to get to the shoulder ASAP, is a different matter, yes, signals are a good thing.
Here's a pic of my 40's vintage signalstat 700 in my 34 jalopy. I shortened it up to meet my desires, and to run on two filament bulbs require a series of relays. Not a big deal, I mounted it all high on the kick panel out of sight.
Installing ugly plastic hardware store lights will get a swift reprimand from me, the self appointed light police. I have the wiring schematic for the relays if you wish.
Well shoot, wrong pic, as there is no signal on the car, but you see the other pic of a stock, and shortened model 700 signalstat. lots of em on ebay, I have some too