I posted something about this on one of the 919 facebook groups, but I feel like I should post it here too for posterity. I just picked up a 919 earlier this summer. I've been enjoying it with the exception of a few small annoyances, one being the speedometer. The stock speedo reads about 10% too fast, which you can tell if you put your face right up against the cluster and squint really hard. It's better than nothing, but not great.
I decided instead of installing a speedo healer that would throw off the odometer, I'd kill two birds with one stone by designing gauge faces with a speedometer arc that's scaled back along with an easier to read layout. Removing the OE faces wasn't difficult, and scanning them into the computer at 600 dpi gave me plenty of resolution to work with.
I'm still not sure how I'm going to have them made. I already stripped the face off the speedometer plate and I wanted to go riding last weekend, so printed a quick mock-up to make sure the overlay fit and the numbers were placed correctly.
I'm going to need a more opaque black layer for the finished product, but the light diffusion across the white parts looked ok. I verified by GPS that it reads about 2 mph fast across the board, which is a big improvement in accuracy at 70+ mph. I'm thinking maybe I'll try a vinyl overlay for the black part or maybe reverse printing on transparency sheets.