Most likely a 1998/840. That's what Speedmasters in general came with at the time. As for 20/16 taper with friction buckle or 20/18 taper with pushbutton buckle, I am not sure.
Alaska Project was 2008, and I recall seeing a few 2005 3570.50s with the 849 end link that was original. So that being said, probably 1998/849 lol
Ah, yes, you're right. Mine from 2000 came with the 1498 and I replaced it with the 1998. Since I traded that watch away, the details get fuzzy.