shocks for 4" of lift are far too long for 2.5" of lift. they'll bottom out and cause damage to the shocks and eventually rip the shock mounts off the axle.
you can add 4" lift springs, but you'll need everything else required for 4" of lift...adjustable track bars, rear track bar relocation bracket, bumpstop extensions, extended brake lines, extended sway bar links. The SYE will be required for 4" of lift, so good that you have it. You may need to buy a new rear driveshaft if the length is incorrect for 4" of lift. You'll also need to address steering, brakes, caster, alignment, etc. This may require adjustable front lower control arms.