I have noted several differences (see below and / or video here -
https://youtu.be/isSiNiHlONs )-
1. Different color front panels.
2. Several areas of apparent dampening materials added to Runco.
3. Runco has their own video taps off of the board.
4. Addition of a signal transformer presumably for the Runco audio upgrades.
5. Addition of coax audio out and AC3 on Runco.
6. Addition of some unknown to me blue part on the video board by Runco.
7. Addition of dual sided tape to Runco cover as well as adhesive top of flipping mechanism.
8. Addition of some unknown to me white wire and resistor to video board by Runco.
I assume some of this is what they did to correct the APL and picture cut off issues the 900 has...