  We present spectra of three gravitational lens systems taken with the Low
Resolution Imaging Spectrograph on the W. M. Keck Telescopes. All of the
systems were discovered in the JVAS and CLASS radio surveys, which were
designed to find lenses suitable for measuring $H_0$. Previous spectra of these
systems had low signal-to-noise ratios, and only one of the source redshifts
was secure. Our observations give unambiguous lens and source redshifts for all
of the systems, with ($z_l$, $z_s$) = (0.4060,1.339), (0.5990,1.535) and
(0.4144,1.589) for B0712+472, B1030+074 and B1600+434, respectively. The
observed image splittings in the systems imply that the masses of the lensing
galaxies within their Einstein rings are 5.4$\times 10^{10}$, 1.2$\times
10^{11}$, and 6.3$\times 10^{10} h^{-1} M_{\sun}$. The resulting V-band
mass-to-light ratios for B0712+472 and B1030+074, measured inside their
Einstein ring radii, are $\sim 10h (M/L)_{\sun, V}$, slightly higher than
values observed in nearby ellipticals. For B1600+434, the mass-to-light ratio
is $48h (M/L)_{\sun, V}$. This high value can be explained, at least in part,
by the prominent dust lane running through the galaxy. Two of the three lens
systems show evidence of variability, so monitoring may yield a time delay and
thus a measurement of $H_0$.
