For curvilinear rafter tail cuts, the best tool for the job is a portable bandsaw you bring to the material. If you can't spring for one of the portable bandsaws (Mafell makes a nice one), there are options. If you have a shop with a smooth concrete floor, you can get any old 14" shop bandsaw, Delta, Jet, etc, and mount it on a base with large swiveling wheels. It is possible to swivel and move such a bandsaw around pretty well and execute scrolling cuts.
Otherwise, another option is chisels, gouges, shaves.