Power Cleans are recommended because you don't need a very heavy pull to get work in and the power clean keeps you pulling from the floor, albeit lighter weights, quickly to work on explosiveness. Now using deadlifts isn't wrong per se but if you are going to use them you need to consider two things:
1) Squat volume - squats and deadlifts should not be viewed as separate lifts and rather cumulatively since the stress on the hips and low back from both lifts overlap
2) The volume pulls should be sufficiently lighter than intensity pulls. I'd say ~75% with a variant that makes the light weight more difficult (e.g. RDLs, paused pulls etc). Alternatively, you could do alternate partials every other week. So haltings or deficits one week and rack pulls the next.
Honestly though, I think your low back is likely overtrained if you are pulling 20 lb over your squat with both in the low 300s. I'd offload the squat more so you can get that deadlift up to where it belongs.