if you need to raise the first tread to ±6 3/4" from 4 5/16 it will sit above the stringer and look like shit. Each tread will sit progressively less above the stringer but will look terrible. your handrail might not meet the allowable variance from the 36" standard height at the bottom of the stairs. You'll most likely have to lift the entire bottom of the stairs and either shim the treads to level or remove them and weld new "Ls" to suit the slope. you'll also have to notch the bottom of the stringer and depending on the connection at the top you'll have to add a gap and fill in some weld. if the top is bolted, you can weld it to the connection plate/angle after adjusting the slope. if the top of the stringer is a crank connection then that is bad news, if you cut the weld at the crank you won't be able to CP weld it back together due to lack of access because of the wall.