As long as you only cut the welds and not into the metal of the perches or shock mounts you'll be okay. When you get the u-bolts from the F150 also get the spring pads that clamp the springs down, you'll need those. Just because your not buying new perches doesnt make this way "wrong". Lots of people just prefer fresh new parts for everything. I plan on reusing my perches too, but I dont like the shock mounts.
I wished you lived closer I'd sell you my complete stock 4.10 28 spline 8.8 axle I just took out from under the ranger.
2004 Ford Ranger 2wd Edge Stepside Regular Cab