i think the boost compensator adjusts the governor lever to alow more fuel and the altitude compensator moves the governor lever to cut the fuel.
does anyone have a pic if the 5l pump with cover off? i can throw up a pic of the boost compensator cover.
would be good to know if it fits so i dont have to pay the specialist.
here is the inside of boost compensator

and this is the 5l altitude compensator
http://img820.imageshack.us/img820/382/img0439k.jpg
picture is not the right one but the principal is the same