Non A-body mopar question

1968 Dart 270 said

All very valid points. You're right. I have no idea what the previous owner drove like. Just that I've tried to be gentle on it since I've owned it. I understand too that they weren't expecting people to still be driving them 50 some years later or that many would have 200k plus miles on them. It's just a shame because the weak link on these a bodies is the rear ends. Everything else is pretty much bullet proof if not abused

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The short answer is the 7.25" would've been std. equipment for Slantys & 'teeners, You could always option up in those days, so finding an 8.75" behind them is surely possible as well. 8.25" rears didn't appear 'til '72-'73, so there's -0- chance that was an option in Your prospective ride.
FWIW, I beat the crap out of My '69 Dart Custom w/the Slanty including multiple neutral-drops for over 3yrs, then dropped a cammed 'teener in it & proceeded to burn the piss out of the pass tire with that bootleg 7.25" rear. I left clouds of tire smoke drifting over the cornfields on the ridge, for about a year(w/an auto) I pounded that thing, then I pulled up in front of some other friends of My Bud riding shotgun(BIG guy)...I blocked it up ready to put on a show & 'POP'!!! LOL........later it got a 4spd & 8.75"......but when I pulled the cover..there was almost no gear oil in it...duh...no signs of leakage ever but, who knows if it had been full of lube???