I can' really help ya, it looks like it has a lot of HI characteristics but I think they were always marked. I could be wrong.
There are lots of khukri's made in that region obviously, everything from tourist junk to HI of the heap quality.
That certainly looks like a very good one.
Hopefully someone wiser than I (ok, that's just about everybody here) will come along with some useful information.
The fact that it came from your grandfather makes it priceless in my book regardless.