looks like a nice blade. any markings?
grips were also made from hardwood, so wood, er, would also be traditional.
there may at some point also have been a brass or steel bolster and a butt plate with the end of the tang protruding a bit & peened over a keeper. the hole down the centre was also traditionally filled with 'laha', a nepali cutler's thermal cement made from tree resin and dung, brick dust, etc. (there's a thread here on recipes for it & less smelly equivalents)
whatever you do, do
not grind off the rust or use acid, naval jelly or similar agressive chemicals to derust.
use the search function here for info on khukuris, rust removal, restoration tips, etc. there are also a number of threads on identifying your model, showing the grip details of each so you can be more accurate.