Congrats to Lew for having such a beautiful Keris pandai saras.
I think this is a Pattani keris, judging from the hilt style and the greneng.
I think this is still a 'san-mai' construction keris, with the softer steel outer layers sandwiching a harder steel core. There is a difference in the surface condition (different extent of pitting) of the cutting edge and the central body.
The outer soft steel layer could have been made from a file, in my opinion, because of the cross-hatching on the central portion of the base, and on the high point of the gandik.