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We present spectra of three gravitational lens systems taken with the LowResolution Imaging Spectrograph on the W. M. Keck Telescopes. All of thesystems were discovered in the JVAS and CLASS radio surveys, which weredesigned to find lenses suitable for measuring $H_0$. Previous spectra of thesesystems had low signal-to-noise ratios, and only one of the source redshiftswas secure. Our observations give unambiguous lens and source redshifts for allof 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. Theobserved image splittings in the systems imply that the masses of the lensinggalaxies within their Einstein rings are 5.4$\times 10^{10}$, 1.2$\times10^{11}$, and 6.3$\times 10^{10} h^{-1} M_{\sun}$. The resulting V-bandmass-to-light ratios for B0712+472 and B1030+074, measured inside theirEinstein ring radii, are $\sim 10h (M/L)_{\sun, V}$, slightly higher thanvalues observed in nearby ellipticals. For B1600+434, the mass-to-light ratiois $48h (M/L)_{\sun, V}$. This high value can be explained, at least in part,by the prominent dust lane running through the galaxy. Two of the three lenssystems show evidence of variability, so monitoring may yield a time delay andthus a measurement of $H_0$.Comment: 8 pages, 5 Postscript Figures, uses aastex. To appear in A.

Keck Spectroscopy of Three Gravitational Lens Systems Discovered in the JVAS and CLASS Surveys