[bouncytruck]

Does the SPID on the glove box list them?

Most likely swapped in from a 71 or 72. My understanding is in 70, they had open knuckles, so you could just swap the disc brake parts unlike the '69s with closed knuckles that required an axle swap. Discs were optional in 71, but all 72s should have had them (*disclaimer - GM wasn't consistent and often used leftover parts from the previous year or parts from upcoming years if they ran out.)