There are also a lot of folks with 1/2" offsets, not to mention the 3" spring relocations. You're welcome to try it, but all I can tell you is that on MY '71 Dart there is absolutely no way you can run a 275 without a 1/2" offset. The only Dart's I'm aware of that run 275's have at least a 1/2" offset and a quarter lip trim. That will be especially true for a lowered car. Also, not all of these cars have the same amount of space. Pre-70 Darts are VERY tight out back, most can't even get a 255 without rubbing. So, its entirely possible the early Valiants have more space than a 70-up Dart.
The 1/2" offset moves the front spring hanger over a little more than a 1/2", so that its up against the frame rail in the front. The offset shackles mount in the same place as the stockers, but they're offset a 1/2" to move the rear of the spring over. That places the spring even with the inside of the wheel tub, so you can run as wide of a tire as will fit in the stock wheel tub. The hangers and shackles bolt on, but you need to move the spring perches in 1/2" on each side, so 42" C-C.
