2.5/4 drop with 255/70/15

[chevymotocross]

I currently have a stock height, 87 swb with p265/75/15 tires. They look good with the stock height but I want to lower it, 2.5 front via spindles and 4 out back via shackles/hangers. I can see that these big tires will rub with that drop. I work at a tire shop, and someone bought 4 new tires for their ford truck, and junked the still very good 255/70/15 Kelly tires. I snagged em . I think these should do fine. I was wanting to actually go with a wide/short tire, like a 275/60 but that will throw off the speedo, cost me money, and I think a 2.5/4 drop won't be enough for a 60 series tire. Anyone out there with a similar drop and the 255/70 tire? Any rubbing or issues?