Mike, it's all up to you. Every service that owned an ambulance painted it whatever color they wanted, so any color (really, ANY color) is possible to be used on an ambulance. And they were often repainted. There's no real "standard" red.
If I were you, I'd check with a paint shop and see just what "Dakota Red #50" looks like on a paint chip. Or look at the spot of the original color if you can find it. If you like it, then that's your color. Done. If you don't like it, look through the book and pick a color you like.
My ambulance, I had the color on the nameplate, and I wasn't sure. But the shop sanded the later color (orange) off the hood and found a decent section of the original color, "Flamengo Red", and I loved it. And that is the red color on my ambulance. It's not what you normally see (it has, to me, a little bit of blue in it), but it looks good.