No problem! So a stock A-body 8.25" is about 56.75" wheel mount to wheel mount, so I would wager that what you've got is in fact a stock A-body 8.25. That also matches up with your drum to spring measurement, you've got about a 1/2" less from drum to spring as I do on my '71 Dart with an A-body 8 3/4 and BBP axles. Which is spot on for the difference between those two rear ends. And you have ~11.75" spring to fender. That's more than enough to run a 245/45/17 or 255/45/17. It's a little short of what I would like to see for a 275. Not saying it can't be done, but you might have to trim/roll the quarter lip back a 1/4" to keep from rubbing if you did that. Anyway, you want about a 1/2" of clearance between the tire and the spring. With a 17x8" and lets say a 255/45/17 the section width is ~10.2" so the sidewall hangs over about .6", call it a 1/2" again close enough (some 255's are 10" sections anyway). So that works out to be a 17x8" with a 4.5" backspace. Which matches up pretty with other 8.25" rear tire combo's I know of. So I would say run 17x8's all the way around. In the front you'd want 17x8's with 5.25" to 5.6" backspace, and in the back you'd want 17x8's with 4" to 4.5" backspace. That would allow you to run 245/45/17's all the way around, or 245/45/17's in the front and 255/45/17's out back if you wanted. Only reason I don't say 255/45/17's all the way around is that's a 26.1" tall tire, and on a Barracuda that may cause issues in the front with the lower front corner of the fender.