Ok folks, life's about to get real again. Anyone have practical experience or recommendations with installing a modern baby seat into the back of this ancient rig?! LOL, thanks!

 

Lap belt thru the seat in the middle. I think also some child seats are designed for a shoulder belt to be routed thru it.

 

I'll probably get flamed but my kids lived so....
I ran two short lengths of chain from the middle back seat down to the seat belt anchor points. Then I used the official Latch belt to hook onto the chain.
The chain was use so I wouldn't have to fish the Latch bwlt through the rear seat every time.

 

Considering that an overwhelming amount of child seats are installed incorrectly, and sometimes it's nice to have the convenience of being able to remove the seat without taking an hour cursing to reinstall it properly, I would recommend a Britax with the clicktight system. It essentially closes and snugs to pick up slack in the seat belt and is much easier to get a nice tight grip without the hassle. We had a Recaro intially and it went back into the bmw that had LATCH, took over an hour to get it in the discovery and once I had to remove it to fold the seats down I wasn't about to travel down that road again. The Britax marathon with clicktight works great in these cars

 

Thanks for the input everyone. Right now the rig is only for back-up pick-ups/plan B, with the Caddy taking the brunt of the planned trips.

There was an Instructables DIY that used eye bolts that looked shady, though I considered it. I found a floor anchor system used on school busses for aftermarket seatbelt installation, so I'm gonna give that a whirl and create my own latch points. Hopefully I can use them in addition to the middle seatbelt.

 

There are 3 threaded holes behind those plastic plugs in the roof lining directly above the rear door, in AUS we use an extension strap that connects to the top of the baby seat with the the lap/sash belt clipped thru the base.
This is as safe as any other vehicle, both my girls used the same capsule from coming home from the hospital up to a toddler seat til 7yo.
1st one in my old RRC and 2nd in the D1, not the best pic but will give you an idea.

 

Probably a good idea to put a thick rubber pad under the car seat to protect the leather seat. On my Jetta leather seats, I didn't really remove the car seat for several years. When I did, I was greeted by an ugly pattern in the back seat where the child seat bottom stretched the leather. I thought it would eventually go away from the heat and so fourth, but we haven't used car seats for 7 years or so and it hasn't gotten any better and looks like crap.

So if you care about the leather on your back seat, find a heavy duty piece of thick rubber or something to put under the car seat to protect it from ruining the upholstery.