Replacement is actually fairly easy, though getting to the three phillips screws to remove the black plastic shield around the accelerator pedal can be a bit hard on the back and arms.
Especially since yours is an 83, make sure that the new throttle cable is the same length as the old one before you start, just in case. I think that the colour of the plastic retainer on the intake manifold denotes the length. You'll want the red one for a B23/230 LH Jet intake manifold if you have one, or a white one for the B21FT intake (longer cable). I assume that you don't have a B21F, and I don't know what cable it uses offhand.
Intake manifold look like this (except not white...bad idea)?

If so, and you haave a red cable end, then you should be good. red cable end is visible in picture just in front of the oil dipstick handle.

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1981 242 GLTi 1967.5 122S
Seattle, WA