For 1970, a B body with power or manual disk brakes would have the line connections inboard.
http://www.imperialclub.org/Repair/Lit/Master/274/page13.htm If that's true for '71, then I'd say they are both wrong for your application. (edit: 1971 is different)
Shop manual will have bore and stroke. My notes say the '70 b-body master was 1.125" bore. Here's a chart Moparts member "Mastershake" created for a Mopar Action article.
http://www.moparts.org/Tech/Archive/brake/14.htmlI know he's made some corrections since then but it looks like the correct master for '71 will have a 1 1/32 bore. Do a some searches on the p/n 3461176 and casting number Mastershake has posted. Then you can compare with the Dorman substitutes.
