There's a few things about this Mustang that make me see a few "red flags":
The interior has an overhead console with black in the middle. They all had wood applique in '68.
The Seat colors don't match the rest of the interior. The headrests look like they are '69 type (shoved down on seat) with the cording on the ends.
The windshield pillars have padding, and yet the rear reflectors are post Apr. 26th.
The lack of hood pins (factory ONLY), tells me that it was either hit in the front and never replaced those parts, or "if" this car is not legit, those pins and especially the retainers are hard to get (or know where to get them).
The 302 looks kinda like it's a post-'70 motor. New type A/C compressor and belt. Look at the temp sensor on the front right of the intake...it looks post-68. There is a chrome shock tower brace, too. Non-Stock.
No screens on the side scoops. I can't see any witness lines on the scoops, either.
The slotted wheels painted body color "was" done, but very rare...lots of cars today have that repainted.
$13K? Hmmm.....
Paul.