Yep, call Hornady. +1.
For others in a similar situation, generally you can safely use the starting data for a bullet of the same, or next-higher, mass, and then work up from there. I had to do this for some of my cast boolits 'cause there aren't any published load data out there for 'em.
Traditionally, 7.62x54R didn't get a lot of love here in the USA 'cause of the cheap (and yes, good quality) milsurp, and the low numbers of Mosins. Given that these rifles are now increasing a lot in popularity ($100 full-power .30-cal rifle?? Heck, yeah!), I suspect that we'll see more load data for this round as time progresses.