1991 diagrams list a canister purge valve (LHD only) so that's definatly what the box and valve are there for.
Yes the 2.0 Pinto ISCV should be fine if it's in good working order. idealy you should find an original DOHC intake pipe and modify that to fit between the filter and the inlet elbow as this has
Having reviewd the diagrams, the 3 pin is indeed the fan plug.
The Brown is the ground
Black+Red is fan one supply
Black+Blue is fan two supply. ( ignore this as you have one fan.)
Fan one should cut in first, sometimes we swap for escort Diesel temperature switches as they cut in at a lower temperature.
TT