The D70-14 was the minimum size required on Darts & Barracudas with disc brakes & I'd "assume" they were blackwall "SPEEDWAY"s.

Do you have any other pics, front or rear & any showing tread?

The 7.75-15 were probably blackwall "POWER CUSHION"s.

I doubt they would've turned a more costly "blue dot" or "red stripe" around. They were just cheap "rollers".