A quick rundown of the inner fender extension filler plates over the years.
1970-74
#479094 RH / #479095 LH.
Short strengthening rib pressings. Full main rib-pressing. 4 holes only. Full-width bottom fold with strengthening pressed over corner.
No stamped GM part numbers or details. Reproduced.
Firebird 70-74 fender extenion fillers rust treated 479094 479095 (2) by
Ben, on Flickr
70-74 Firebird fender filler extensions used 479094 479095 (3) by
Ben, on Flickr
70-74 Firebird fender filler extensions used 479094 479095 (2) by
Ben, on Flickr
70-74 Firebird fender filler extensions used 479094 479095 (9) by
Ben, on Flickr
1974-76
#547419 RH / #547420 LH.
Pressed strengthening extended. Full main rib-pressing. Clearance holes for fender-radiator support bolts, smaller holes to secure directly to radiator support. Full-width base fold has become outer-end single tab mounting to fender base.
Used GM-only, not reproduced.
Firebird 74-76 fender extension fillers 547419 547420 (1) by
Ben, on Flickr
Firebird 74-76 fender extension fillers 547419 547420 (2) by
Ben, on Flickr
1977-78
#10000818 RH / #10000819 LH.
As per above style. Full main rib-pressing. Lower folded bracket has become central single tab mounting to radiator support.
Used GM only, not reproduced.
Firebird RH 10000818 fender extension filler (5) by
Ben, on Flickr
Firebird RH 10000818 fender extension filler (4) by
Ben, on Flickr
1979-81
#10007269 RH / #10007270 LH.
As per above, central mounting tab only but full main rib-pressing now half-rib, flat at top to match 79-81 inner fender removed rib-pressing.
Used GM only, nor reproduced.
79-81 and 77-78 comparisons.
Inner fender extensions powdercoated 79_81 10007269 top 77_78 bottom 10000819 by
Ben, on Flickr
Firebird fender extension filler plates 77-78 10000819 79-81 10007270 LH (2) by
Ben, on Flickr
79-81 Firebird fender extension plate powdercoated 10007270 (1) by
Ben, on Flickr
79-81 Firebird fender extension plate powdercoated 10007270 (3) by
Ben, on Flickr
1980 Assembly diagram modified from earlier years by alteration of lower central tab but maintaining full rib pressing in pic.
Also removed, 1 of each top fasteners, leaving plate held in place by one screw into radiator support and one at base into radiator support only. Production line seems to have ignored this, even on low-mileage original vehicles, keeping 2 bolts through the lot, washers over the clearance holes meant to sit over them, no screws into radiator support, plus single bolt at base tab. Instead, line up inner fender and filler plate by inserting rubber hose into the smaller holes matched on both until bolts tightened.
1980 Firebird fender extension filler panels diagram by
Ben, on Flickr