I know People can use Photo shop to create this from imagery. just needs to be saved out as a DXF or other Vector image to be able to be converted to machine code.
I could do it in 3D with SolidWorks if I had a high resolution image of a real emblem the 3 and the 8 are easily duplicated from a 383 emblem the 1 would be the best guess number.
It's all in the Font!
What I would need is an actual 340 emblem correct for the model year. and some example emblems of a 1 from the time to get width and height and post locations.
I also just picked up a 3D printer I am dyeing to try out!