The underhood light was only available as part of the ZJ9 Auxiliary Lighting option - it wasn't tied to or included in any other option package, and the underhood light wasn't available by itself.
When ZJ9 was ordered, there was only one underhood light, although there were four different locations - one for L-6 and 396 without A/C, one for 396 with A/C, one for small-block V-8, and one for the ZL2 hood option. The only reason that RPO Z87 is referenced in the title block on sheet A2 of the U26 option in the assembly manual is that Z87 included the hood insulator pad, which affected the installation; Z87 didn't include the light.