There are several detail differences, Ford revised the lower shock tower welding for later '67 and '68. Then around March 1968 big block shock towers started to get a reinforcement plate.
Fuel line routing changed in mid 1967 model year to avoid the possibility of a broken U-joint causing a drive shaft to cut the fuel line and cause a fire. This caused a modification to the left torque box and frame rail, allowing the fuel line to pass through each.
Radiator core supports have a wider opening for the radiator in 1968 because the widest radiator in 1968 was 24" instead of the 22" size used for '67 Cougars.
Trunl lids on early 1967's have a different reinforcement than later '67 trunk lids. 1968 trunk lids do not have holes drilled for stops at the lower corners.
Door inner skins for early 1967 don't have provisions for the XR-7 inner door handle location.
1967 hoods do not have the fan shroud cutout located exactly the same as 1968.
Early 1967 rear license plate frame / gas tank doors are a different stamping than later ones.
Ford changed thousands of details all through the 67 - 68 production run. Most of the details were running changes rather than tied to a model year, aside from the obvious styling cues and safety upgrades. There is no end to the differences between 7F91S500001 and the last '68 Cougar produced. If I knew all the differences I coumldn't type them in a 8 hour day.
Well i know that people have told me that the '68 cougars are better for putting big block motors into... i just wanted to know some of the differences between the 2 years to see how much is different. Looking for a "rough" car to put a 429 in and i was thinking a 68, 69, 70 because i know they put the 390's in them but wasnt sure structurally if the '67 would be up to it.. do you think a '67 could handle the power and torque of a 429 (its a '70 motor) and not have any structural problems?
The '68's have those side marker lights as mandated by law, '67's didnt have them.
I own a '68 but the '67's in my opinion have a cleaner look ..
It's a little pet peeve of mine that those lights are too big in proportion to the car, not that I love the way the '68 looks too but check out other '68 pony cars' like a camaro or firebird, the marker lights are tiny, look cool..
Oh well, theres no such thing as ta perfect car ..excuse me for venting ..
Just find the most rust free car you can to start with. If that turns out to be a '67 just add the torque box and keep on truckin. Lots of people have 428, 429, 460 and bigger engines in '67 Cougars. I have a 454 CI FE engine in mine.