Easy to do, measure your length on the stock forks, from lower tree to axle. Measure the new ones to determine how much needs cut off of them to get the same measurement. Measure inside the new upper tubes for the length of the old tubes to fit into them. Cut the old tubes at the proper length, and insert them into the new tubes. You can clamp or weld them on. Note" inside the new tubes is a seam that you may need to file down slightly to slip the old tubes in. No biggie at all.
I've added front brakes to it since then, another easy mod.