Continuous 40 mile trail near Amherst, MA, from Wendell State Park to the Notch Visitor Center (off Hwy 116).
Note that this guide indicates that the trail extends another 6.5 miles to Hwy 47: https://www.amherstma.gov/DocumentCenter/View/610/Robert-Frost-Trail-Guide But the route appears tentative, incomplete and poorly marked (not marked with the orange blazes of the rest of the route). At present it seems more like an idea than an actual extension of the RFT.
Ran it today in 7:57, not quite what I hoped but a great route. My friend actually set the female self supported FKT finishing in 9:10. She started five minutes after me to avoid any complications with the verification.
Also definitely read Dan Grips notes and I’d recommend running the section from Pratt Corner Rd (around mile 26) to Harris Mountain Rd once before attempting as there are a lot of turns that don’t have obvious marking.