I did change the sys11 sound board on my funhouse to a WPC sound board from the getaway. I also changed to the latest ROMs for sound (L3) and game (9.05H).
Changes as follows:
-Removed old sound and interface board
-Moved W2 to W1 on the CPU board
-New game ROM, 4 Mbit
-New ribbon cable between CPU and sound board
-New ROMs for the sound board, 1 x 2 Mbit and 2 x 1 Mbit needed
-And most important: Made an adapter cable so that the 10 VAC from the sys11 transformer is changed from being full wave rectified to half wave rectified on the sound board. This gives the correct voltage to the sound board.
The connection from the transformer to the sound board has to be changed in the following way (this is done using my adapter cable in the attached photo):
Transformer <-> Sound board
1 <-> 1 and 4
2 <-> 2 and 5
4 <-> 6
5 <-> 7
6 and 7 <-> not connected
This is not a how to, do it at your own risk. I just wanted to show that it is possible. The half wave rectification stresses the components (mainly diodes and capacitors) a bit more but should not be a major issue for home use.