Hazard Lights
Hazard lights are another modern safety feature worth considering. Many older cars can only warn other drivers with their turn signals but this can be confusing as it just indicates that the vehicle's driver is intending to turn. These kits do not seem to be very common but a few places on the Internet appear to carry them. Since hazard lights are standard equipment on modern vehicles, hazard flasher retrofits are no longer as easy to find as they were back in the '60s and '70s, but they can be had. NAPA Auto Parts carries a 4-way flasher retrokit under Echlin FC6401, which looks suitably "olde-tyme" for installation in an old car. You will need to supply the actual flasher and the indicator bulb because the kit comes without them so it can be used on all 6v, 12v and 24v applications. Pick up two Ideal EL12c electronic flashers at your local auto parts store because NAPA doesn't usually have them.
Centre High-Mount 3rd Brake Lamps
Many older vehicles have small and often hard-to-see tail lamps, compared with modern vehicles. Many drivers are not as observant as they should be and may not take into account the often poorer visibility of an older vehicle's brake lights. If you frequently drive your older vehicle, you may also want to consider adding a Centre High-Mount 3rd Brake Lamp. For more information, please also read the Allpar article entitled Hella LED Third Brake Light review.
Turn Signal / Brake Light Upgrade
With LED bulbs becoming so popular because of their brightness and low current draw, many people are replacing their brake lights with LEDs. This is BAD idea in this application as explained in the Allpar article What didn’t work: simple LED replacements. You are much better upgrading to a P3496 bulb or keeping your 1157 bulb. These bulbs are available from a number of stores, including Daniel Stern Lighting.