We have detected the four 18cm OH lines from the $z sim 0.765$ gravitational lens toward PMN J0134-0931. The 1612 and 1720 MHz lines are in conjugate absorption and emission, providing a laboratory to test the evolution of fundamental constants over a large lookback time. We compare the HI and OH main line absorption redshifts of the different components in the $z sim 0.765$ absorber and the $z sim 0.685$ lens toward B0218+357 to place stringent constraints on changes in $F equiv g_p [alpha^2/mu]^{1.57}$. We obtain $[Delta F/F] = (0.44 pm 0.36^{rm stat} pm 1.0^{rm syst}) times 10^{-5}$, consistent with no evolution over the redshift range $0 < z < 0.7$. The measurements have a $2 sigma$ sensitivity of $[Delta alpha/alpha] < 6.7 times 10^{-6}$ or $[Delta mu/mu] < 1.4 times 10^{-5}$ to fractional changes in $alpha$ and $mu$ over a period of $sim 6.5$ Gyr, half the age of the Universe. These are among the most sensitive current constraints on changes in $mu$.
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