Congrats on the SI! I would look for battery acid damage first as the problem. Mine had sat forever, like yours, and the batteries had killed the board. Alltek makes a new board that is pretty much plug and play for $199 and has a built in battery. http://www.allteksystems.com/products-mpu-replacements.html#mpu
Your playfield looks nice. Most of these were played to death and have wood showing in places on the playfield.
The 44 bulbs usually melted and warped the plastics on this game. CPR did a run of these plastics for $145 that probably would be worth looking in to for you. It also gives you a cool topper! http://www.classicplayfields.com/store-plastics.html
LEDS look great in this game--in my humble opinion. I also placed an LED strip in the ball trough to brighten up the playfield. Worked good! Good luck!