E-mail Peter Havlik <peterhavlik@ME.com> in British Columbia, who runs the Pantera Series 9000 Registry. This is for GT-5, GT5-s, Pantera Si and any narrow body Panteras built later in the series. He may have more information on your car. The last time I looked, he had no photo for #9421 so he would be happy to hear from you! It shows the Amerisport s/n and the last known owner (Roland Au of CA).
His registry is also on POCA's Web Site, which has a pdf copy of an Owners Manual for a GT-5. As mentioned, it's mostly like the earlier red cover manual but the wiring schematic includes the heated rear window and the later Veglia clock used on later cars. The Illustrated Spare Parts List also covers Panteras up to 1987. Both are downloadable but require membership.