I need to replace 1 (one) bulb in my console on the gas-guage side ('69 RS). Do these plug into the back of the guage, or is it not that simple?

Can someone give me a clue as to where to start?

Ignore this question. 4-screws remove the guage cover and two more remove the bulb cover. Since I purchased the wrong bulb, I'm off to the auto store to pick a new one up :-)

I presume you found the bulbs were inserted into plastic holders than connect to the flexible PCB. One extra bit of advice I would offer is to inspect the metal contacts of the socket to see if they're corroded. If so, take a small bit of rolled-up sand paper and shine them up a bit. You may also want to bend the contacts a tad to tighten them up. You can use a bit of extra fine sand paper or scotch-brite to scuff the copper pads on the flexible PCB as well. Just be careful not to over do it, since there is very little copper on the flexible PCB.

Once verything is shiny and corrosion free (at least at the contact points) put a tiny dab of dielectric grease on those contact points to prevent future corrosion and make the sockets much easier to install. Just keep in mind that the bulb gets pretty warm, so you want to be conservative on the greasing to prevent it melting out and making a mess. This should make your bulbs a bit brighter and much easier to remove without damaging the flexible PCB in the future.