I like the looks of the long version and think it would be better for a rifle length barrel.
I remember reading an article by Bob Milek, probably in the 1980's, where he stated that if the 7.62x39 had been easily available that he and Steve Herrett would never have modified the .30-30 case in the first place.
Good luck with your project, and please keep us posted as to the results.
Robert