From the graphics style and application technique I would say early 60's. Especially due to the box lining, this sort of hand work went away later, especially on the subordinate models.

The brake calipers may be original, I cannot tell what the stampings on the outer arm is, Dural Forge is before Racer even though they are the same basic casting, and brass bushings are before the plastic for example.

Many of the other parts look replaced as you mentioned.

Value? No telling, worth keeping the original paint? Yes, Worth investing some time and effort, Yes.