Rick, thanks.
Just take the upper seat back off. An allen key takes off the latch knob, then 2 screws along the bottom. Pull the bottom of the back out a little bit( to clear), then slightly up to release the upper hooks from the back. Then look in. if you see the metal springs and bars and see burlap, then you have the older style. If you see the back of the foam, you have the newer style.
So my early 69 (Oct of 68) had the metal frames. I also have two sets of deluxe seats (weeks 3 and 4 of Jan). I checked the week 4 and it had the newer style.
There were a lot of changes in the Nov/Dec/Jan timeframe (kickpanels, seat foam, headrests, etc) and it is tough to pin down a specific build week as it depended on how much stock in hand and what the installer pulled.