A big part— actually, the biggest part— of the A-Body's longevity was this hunk of metal under the hood: the Leaning Tower of Power, aka the Chrysler Slant-6 engine. Production of the Slant-6 for U.S.-market vehicles ran from the 1960 through 1987 model years, and I have photographed dozens of discarded ones in recent years. This one displaces either 170 or 225 cubic inches (2.9 or 3.7 liters, respectively).
You could get a 273 or 318 V8 in the '68 Valiant, but most Plymouth shoppers wanting something quick went for the very closely related and much sportier-looking Barracuda. Since this car has the automatic transmission instead of the bargain-basement three-on-the-tree column-shift manual, chances are that the original buyer sprang for the bigger 225 Slant-6 as well.
The interior is on the worn side, but doesn't show the nuclear upholstery devastation that Colorado cars suffer when forgotten for years outside.
The body damage on the left front and right rear suggests that the car was involved in an unfortunate chain-reaction collision.
Cool as a 1968 Valiant may be, a six-cylinder/automatic car with four doors isn't worth restoring unless it starts out in very nice shape. Crash one hard, and a place like this is its next stop.
This Chrysler dealer-training slideshow for the 1968 Valiant features a Sonny & Cher soundtrack.