I am in the process of acquiring components to put a LCD in my POTC. Here's my take on it from the reading I have done. The LCD draws enough current that it doesn't seem wise to draw off the games 12v. So, if you're going to have 1 wall wart for the LCD, you might as well power the Pi with a 2nd wall wart. Here is the single, most usefull post I have read in making sense of this whole thing.
https://pinside.com/pinball/forum/topic/smartdmd-color-display-setup-guide
BTW, I once had a DE Batman power supply board go up in smoke with no mods on the game at all. Burnt a hole right through the board.

I am in the process of collecting all the pieces to do this to my POTC. I have read the posts about increasing the max temperature setting. Since heat is an issue, I was wondering if the heatsinks they sell on ebay for the Raspberry would be wise to install to help safeguard the electronics. Also, I was wondering if the heatsinks will fit under the Smart DMD adapter board. If not, the heatsinks could be trimmed down a bit and it would still be better than no heatsink at all.

OK, will do, thanks.

Can the Raspberry be powered by the USB port on the SAM CPU/Sound board? I looked in the manual at the schematic and there's +5v there. If so, all it would require is a simple USB to micro USB cable.

OK, I'm going to be the guinea pig. If my CPU board blows up, oh well, people will know not to do that. Here is my logic on why this should be OK.
1. The 5V circuit is protected by a 4A fuse in the unregulated 8VAC line
2. The LM338 regulator is rated at 5A constant, 7A peak
3. Several people are running the Pi off from the J11 power input to the CPU/sound board
4. The L3 that is in series to the 5V on the USB port is rated at 1100ma
5. The Pi draws around 500ma with a max of 700ma
6. The coin or tix meter is run off the 5V. Although it's an intermittent load, the power circuit has to be designed to support it

I will take temp readings on the bridge and regulator for the 5V, before and after install. I will also take voltage readings at the 5V test point before and after. Although the LCD should still be run off a separate power supply, it just seams really simple, clean and cool to just plug the Pi into the USB port.

WooooHooo!!! It works!! Went for it and plugged into the USB port. It's been running for a couple hours. All temps are the same as before and the 5v is the same. The Pi powers off with the game and boots up properly on power up.