To perhaps clarify, the VFD I'm using, and all the other ones (k610a, 7000-series, 3900-series), are essentially the same as this one (k612a). They have different resolutions, physical sizes, brightness, command sets, serial speeds, etc, but they're all serial-driven graphic displays and all support drawing pixels, lines bitmaps, etc. The display is sent commands by software on the empeg and does what they say, it's not asking Hijack for an image, decoding it, and showing it autonomously (although you could probably sort of do that with the 3900s in theory, lots of macro support).

Basically I have a general API of drawing functions, and an implementation of it for my 3900 (and almost the 7000, since the command set is nearly the same). A quick-n-dirty port to another display is just implementing the drawing functions for that display and linking them in instead of the 3900's. Then you go back and figure out why it doesn't work, and then you go back again and find different ways to speed things up with the different features each display supports (for example.. some can draw in XOR mode so you can just send the changed pixels and say "toggle 'em all", others can't so you have to specifically set each changed pixel on or off).

And to clarify slightly further, don't panic, the circuit board full of stuff in the pictures is just a switching power supply (that powers the controller and VFD) and a bunch of junk required to take the joystick/button input and send out character codes down the serial line to the Empeg. The VFD itself just takes power from it and passes the receive line through to the Empeg's transmit. You could possibly get away with no real power supply since this model is 12V instead of 5, but it has to tolerate the noisy and variable 14V output of a car. Or you could use a simpler/less efficient regulator that just burns the voltage off as heat.