Both methods will work, but there are a couple of issues to be aware of.
Brightness. Does the car have a dimmer control to adjust the brightness of the bulbs to suit driver preference? The choice of the series resistor may have some impact on the LED brightness, but they will basically be on full brightness or off. You would need to build a small PWM circuit to control the LED brightness.
Colour. The original peanut bulbs will probably give a yellowish warm glow, but the LED's will give a cold bright white glow. You may find this annoying compared to the rest of the dashboard lighting.