101 Track Plans was first published in 1956, IIRC. N didn't exist. The figures for N were added to later editions simply by halving HO figures. Those curves are supposed to correspond to HO 18", 24" and 30". In N, those should be about 9.75", 13" and 16.5". The track centers were derived from Westcott's standards of 2.5", 2.25" and 2" for HO. So you may get some sideswiping with using his spacing figures on those curves.
The Track plan book 101 Track Plans for Model Railroaders gives N-Scale track centers for the following
Sharp 1.25 (16.7 scale feet)
Conventional 1.125 (15 scale feet)
Broad 1.0 (13.3 scale feet)
Straight tracks as close as 13 scale feet from center to center
It defines minimum curve radii as
Sharp 9 inches
Conventional 12 inches
Broad 15 inches
Fan of late and early Conrail... also transition-era PRR, 70s Santa Fe, BN and SP, 70s-80s eastern CN, pre-merger-era UP, heavy electric operations in general, dieselized narrow gauge, modern EFVM and Brazilian railroads in general... why bother trying to list them all?