I don't know what Belvidere Rd. is. I have a 70+ mile route that starts in Frenchtown and goes to Belvidere via Spruce Run S.P. and Washington. It them comes down the river on the NJ side using Foul Rift, S. Foul Rift and River Rd. to P'burg. Then Carpentersville Rd. and down the river to Milford and back to Frenchtown. I also go that way along the river when I do three-day tours from Pt. Jervis, NY to Philly.
MR. B - A bike ride in Frenchtown, NJ