Thanks ChipMcK for that. Thing is I don't remember an installer app for Lion or anything before 10.9. Everything I was buying/downloading was coming as a big DMG which allowed you to burn it directly on a DVD and boot from that. Pretty straight forward, that's why there was no need for this script here. Anyway, I'll take a look at the contents (thank you) and see if they are somewhat similar to the installers for 10.9.x up to 10.12.x (you can forget 10.13, that's a different beast altogether).
Having said that, while searching my archive HDs, I found an app from 2013 that seems to deal with this particular issue (and a whole lot more, like updates);
InstaDMG. It's a project that started in 2008 and abandoned in 2013. It uses the Apple's installers and subsequent updates to create a single up-to-date image for installation. I'm not sure if it will do what you're looking for. Its successor,
AutoDMG supposedly works for OSX > 10.8, so it might not do what you want. Be sure to read at a minimum the
Getting Started and the
FAQ. Take a look at both of these programs, since I don't have an installer app to test it.