Question about tires for a 68 dart

I believe it came with a D70-14 which I believe is a 195/70-14. Kind of a thin tire.

The upgrade back then was either a E70-14 (205/70-14) OR A
F70-14 (215/70-14),little more rubber on the road.

If you are looking for factory original replica tires,whether it be a red-line or two white stripe tire Coker tires has them in the D,E,F sizes.
I believe there website is www.cokertires.com

If you are looking for a 205/70 or 215/70 size most people like the BFG's,Goodyears,Kelley,Firestone etc,available antwhere.

Guess it depends if you are stating completely stock or not.

PS: Stay away from bias-ply tires. They handle like crap.
Go radial if you can.

Nice car by the way!

Good luck.