First did you try the search feature? Believe the question about paints types and suggestions has been posted a few times
The method of application depended on the part and year. IF it was a brush application then there were many different types of brushes but most can be applied with a 1/2" chip brush and a fine tip art brush. Or for the last just use a match from a match book if you can still find one of those - if not a tooth pick cut and smashed will work. Holding the wider brush at an angle to the surface during application or pressing during contact will decrease or increase the width to get the finished look you are looking for. Yes you do want to try and do it in a single pass like originally done. If its not perfect - then it likely will look more original
I find that enamels work the best on a oil free surface so paint marks go on before a protective coat of oil does. This helps them stick and works to protect them. The paint IMHO was likely a glossy paint which flattened and softened its look over time when exposed to the elements. ' The makers of these parts - didn't "have paint sitting around" since they were doing thousands of these items so they likely purchased paint in 5 gallons or more containers, not the little hobby or pint containers we would be buying today for our single car
As for your specific marks - never seen yellow stripes on 65-66 strut rods. That is on original cars - only one "restored" ones
Have seen daubs instead at that location
Coil springs, as mentioned numerous times in earlier threads were applied with the spring out of the car with a fairly dry (can make out the brush tips at the end of the stroke often) brush in a single movement, typically from what would become the bottom of the spring to the top. Coils were either sitting on the flat end of the spring or on their sides as runs often appear to travel up hill once the spring is installed
