1FN denotes 85-87 model. Clymer manual has wiring diagrams for all models as I recall so you should be okay regardless of which engine you have. I can’t say for definite but wouldn’t have thought there were many or even any differences between the FZR750 engine & the FZ one other than the fact yours is an early model so should have 2 crank sensor (one either side of engine casings) & later 2MG engine only had 1.