Aftermarket part rant
I feel your pain. I ordered a new single-pot master cylinder for the Valiant, it was the last leaky thing on the brakes to get fixed. Got it from O'Reilly's, but the mounting plate for the firewall was mirror imaged on the unit. It wouldn't bolt up. I took it back and spent 30 minutes explaining to the high-school clerk why it wouldn't work, she never got it. Ordered another one, it was the same thing even thought he part numbers matched and the photo in the computer was correct. Hard to educate someone whose starting point is, the computer shows this, so it must be right... (sigh).
Went to Napa, ordered the same part at twice the price but at least it was the right unit and went in without an issue. Sadly, it seems any parts person under 50 or so is computer-savvy but an automotive moron.