If I put together an 11.5" upper and weld up the chamber, making it unable to fire, can I put it on My pre-ban Bushy and hang it on the wall ???

why??

I believe you would be legal as this is similar to the UZI dummy barrels people have.

However, if you get it wrong, you're looking at 10 years in the pen.  You should write a letter to the ATF technical branch and get a ruling.

Yet another WHY?
If you really want to, get someone that cast their own bullets to fill the barrel/chamber with lead.

I am not sure, but my thought is that since the receiver is the regulated part of the weapon, wouldnt you have to make the receiver unusable?  Because you could conceivably replace the upper receiver and use the same barel and fire it "readily" which is usually the wording the BATF prefers and that is usually open to scrutiny.  I am not an expert, but that is the logic I would use.  (I would hate to see a preban go to waste, so if you are going to do that would you be interested in trading your preban for a post-ban lower and some cash.  Just seems like a waste to me.  If you are going to make it useles, then you can use a pre or post ban receiver.  I am serious about the trade and cash though.

Instead of wasting your money on an 11.5 upper to simply trash why dont you just go the next step and reg. the lower and have an SBR.  Still hang 'er on the wall AND shoot 'er!  $200 more bucks of course but.............

[ROFL2]

My pre-bans are not for sale at any price.

As a collector I think it would be nice to have an XM177E2 replica. I don't have to go thru the hasstle and expense of a SBR.
If I'm going to shoot, I'll use the M4 or 16" CAR upper.

I remember semi auto UZI's came with a 16" barrel and a 10" dummy barrel for looks.
That's kinda the idea here.