no the 87 grill wont work in the 82 header (80-83 regal) , the 84-87 header panel, headlamp bezel ,corner turn signals and bumper fillers are different
fenders, rad support and bumpers are the same from 80-87 so the parts you'll need for the changeover to 87 look are the 84-87 fiberglass header panel, 87 grill, 84-87 bumper fillers, 84-87 headlamp bezels, 84-87 corner turn signals..
depending on how well you shop around (get lucky at a junk yard) you could do this cheap or spend a fortune
if you want GN front end parts expect to spend some $$$$ as these parts are usually the parts damaged in an accident and growing scarce and insurance companies , if NOS cant be located they have no choice to pay big$$ for whatever they can find OE first , then if no OE can be found they will consider repop , they know it will take a small fortune to get NOS which has driven up the insurance on our cars ,
the GN header doesnt have a hole in top center for the emblem so they usually bring much more $$ than a regal/T header (500 on average for a used undamaged GN header) , and the fglass repro header is lousy , ion the cheap find an used 84-87 regal header and fill the hole (still going for 125+ these days )
the 87 grill is a one year only ,OE 87 gn grill is discontinued so as NOS they aren't cheap , there is a black repop that is cheaper than OE (still pricey for what it is but it is a good repop which helped to drop the climbing prices of OE ones a little which were asking GM over 700) , because new is so pricey even good used black grilles go for good $$,
on the cheap the 87 chrome grill used on all 87 other models is the same style as the GN .. if you wanted you could paint a chrome grill and save some $$
the headlamp bezels disc and NOS are $$, used black ones are usually ok sometimes needing a repaint to freshen them up , used chrome are the cheapest ..,there are repops but not for someone with a budget (same guys who make the grill make the headlamp bezels)
new turn signals wont be cheap either as one side is discontinued and no repop yet
GM front fillers are now discontinued and as NOS prices are rising.. I would expect around 200 for a pair to be a very good price (ive seen ads asking for 350pr) . used ones even if they look good will fall apart and aren't worth the risk for what youll pay + shipping , there are fiberglass fronts that arent that bad and the price isnt too bad either (under 100 pr shipped)
once you have the parts its just a matter of getting them painted and bolting them in