Wiring in a stereo using adaptor PC2 17-4

Hello folks,
A friend has asked me to install her stereo in her Daihatsu Hi-Jet. Having read a number of threads regarding the options to do this, I'm left with a question. Using the recommended adaptor, the connections I believe should be used, already have have connectors and wiring in them. Just wanting to check if its ok to proceed with the install?
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There is also the old wiring setup, pre wiring looms, but it would be a shame to chop the loom to do the install.
Any advice greatly appreciated.

I'm of no help right now but I've a little Jap radio to take out of mine & it'll be replaced with something of marginally more sophistication! I've speakers to fit since the little radio that's in it has speaker built into the head unit!! (classy!)
Will keep an eye on this thread as I get going!