the valve in the pic is the low side, the high side is up front next to the condensor. you can get R134a couplings to work with the hoses you got. you could unscrew that silver R134a fitting, but be careful; i've ran into one not having a valve below that fitting (which will empty your system if you take it off)

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1983 300SD (daily driver)
1991 420SEL (work in progress)
1979 300SD (future replacement for 83 SD)

RIP:
1983 300SD (totalled)
1986 420SEL