Is there a drop in bullpup housing for ar pattern rifles? Are there stripled uppers that you can assemble?

Would think that would only work an a gas piston operated upper. I looked up stripled upper and not sure what that is

Pretty sure he meant 'stripped' upper.

Are you looking for bullpup butt stocks? HERA makes one but I have no personal experience with them. It reminds me of a FN PS90 stock. I am not sure who makes them but you can get a 5.7 upper for your ar-15 which uses the PS90 magazines(so the magazines will mount on top of the upper receiver) and then the standard ar-15 lower/mag well acts like a funnel to drop spent casings directly under the gun.

I think a couple places have come up with bullpup converstion units for AR's, but I don't remember any of them really catching on.

If you want a bullpup, but a bullpup. I am a big fan of the AUG.