You can substitute the #81 for the #63. It's the same size but double the candle power. My experience with 6v LEDs is quite different from Tim's. Admittedly it's been a few years but the available 6v LEDs were dimmer than the incandescent bulbs. Perhaps there are more suitable bulbs on the market now. Edit: I just did a quick check and found
THESE BA9 base 6v LEDs that would fit the dash lights. The stock bulb is the #51 which is 1 cp. The LEDs are 13 lumens. To convert lumens to candle power you divide by 12.57 which gives the LED a candle power of 1.03, virtually the same but with a much narrower beam angle. i wasn't able to find any BA15 6 volt LEDs on that site. Perhaps I wasn't using the correct search terms. Bottom line don't assume that a bulb is brighter just because it's LED. Do your due diligence. BTW if you're wanting brighter dash lights you can substitute the #55 which is 2 cp or do what I did and use #316 bulbs. They are a tad longer with an elongated dome but will fit and they are 4 cp. They make quite a difference to my old eyes in the dark. Good luck.
Edit #2: Painting the inside of your tail light housing with gloss white paint and using a plastic lens instead of glass will help with your light output as well.
