Brake line: 8.75 vs 8.25

I don't suppose there's a way to identify the original vehicle? I haven't seen any stamping on the tube itself, just on the third member, which doesn't necessarily say anything about the original car. Other than being a 741 case with 3.91 gears, that's the extent of the facts I have.

First is confirming that it's an A body rear.
Use 72bluNblu's chart to figure out what it's from. It's not uncommon to have a transplanted B body rear in an A body.
An accurate 8 3/4" rear axle width list
Then order the year that's appropriate as determined by the vent location.