Is that 430k total NFB resistance? Looks like a 330k was added in series with the board-mounted 100k (the resistor-to-ground part of the NFB divider is the standard Marshall 4k7, dangling off the opposite side of board as the 330k). If so, that's not very much NFB. Does the Presence even work very well?
My guess is that the person did not have the right value pot (usually 25k-L) and just used what they had.
EDIT: and FWIW and IMO, just based on the photos you posted, there is not a lot going on in that amp. Pretty much any tech (even a hack like me) should be able to hook you up.