^^^^Yeah, I just linked that thread somewhere. I'll find it.
The plastic stacker steppers I know have been used by 0311. Yes, I think the average ones they would have in a gym should be strong enough. Especially considering the weight is a little bit more spread out on them when you squat rather than 250 pound individuals "aerobicizing" on them. Just make sure they won't move around.
As far them taking pressure off the knees the answer is yes, no, it depends, etc so on

. If your knees are bothering you than I wouldn't go right to box squats because while you are getting the trick of them your knee could get worse. It also is going to depend on the box squat height.
Now I recommended RDL's to pity based on what he has available. I would like to point out that in that equation the single leg variation is just as important. He's doing step-ups after his deadlifts...a good day.
You could also try pull-throughs. I know you've been doing at least a bit of glute activation so light pull throughs with a focus on hip extension via posterior chain with a stable back would be good to start with as well. RDL's are certainly a choice. A few people here work out at home so of course they will vary based on that as well, and not just pure choice.
GHR's ghetto style are going to tend to cause some knee discomfort but for most if you just take it easy with them and build it slowly the knees should adjust. Pain of course is unacceptable. I'll let the individual be the judge of what is pain and what is discomfort. If Pity says GHR's hurt his knees and he doesn't want to do them, I've no problem with that. But I will warn that some discomfort is to be expected but doesn't necessarily mean you need to scrap it. If your knees are currently bothering you then I would say no to GHR's right now.
I don't think switching programs entirely because you experience some knee pain is the answer. It's going to happen now and again and you just need to make some adjustments. I think people are becoming very rigid with the idea of progression. There just comes a time when you have to rearrange, add, take away, etc. You want to try and give everything a good go make some progress, at least when you are doing this standard type of strength/mass stuff. But if you need to replace an exercise or change one varitation for another to protect you knees or you just aren't progressing anymore don't worry about it. Just do it. You certainly don't have to switch to westside just because you want to do reverse hypers or GHR's
Obviously you do a lot of deadlifting so of course the PC is really getting worked. But that does not mean that hams strength is getting addresssed enough, for intance, to keep the knees happy.
70 percent of all my "lower body" work is PC stuff, btw. If not more.
You might want to stretch the quads a bit if you aren't already. If your aren't already doing the mobility warmup it would be a good idea...those dynamic stretches that involve lunges and such....this will help the knees and address hip mobility and also make sure that the knees ARE thouroughly warmed up. Do some extensions just with air as the weight to help get blood into the joint.
Are your ankles mobile enough? Are the calves too tight? This can lead to knee problems.
Just a few things to ask. There are lots of things that can be considered when it comes to knees. It's all connected of course in the end.