I have heard that it's possible to get a hot-rod like sheen on metal
through some combination of spraypaint and WD-40... I can't find any
information on it online.  Anyone know how to get that retro hot-rod
sheen?

Elbow grease.

A quality paint job with multiple coats-- about 15 or so-- and
clearcoats and polishing should do nicely. Anything else is a shortcut
and, as such, will quickly fade.

With proper work you will have a reflective shine clear to 18 inches;
that is, holding a ruler to the paint you will clearly see the
reflection for 18 inches. Shoddier work will give you a 6 to 12 inch
reflective shine and won't last.