First of all, pictures don’t work so you should rework those.
Onto the main issue. Removing he dash and the blower is not really going to help you. The plug is plenty accessible just by removing the glovebox. It should be on the RH side.
As far as the s15 motor -> s14 chassis goes, I’m not 100%. I know the plugs are more likely than not different and you’ll have to source a plug from the engine harness side from an S14 and repin it. Only 5 or 6 wires from that plug are needed (vehicle speed, tacho, engine coolant temp, start signal, ground, maybe one more)
I’ve made countless harnesses for s13’s, z32’s, etc with various motors. Take your time and it’ll turn out nice like this.
