Quote from bs2167:
I know you said no restrictions so this is probably redundant, but you can short stocks in that thing? I guess my question is how difficult is it to find a broker for such a set up? (e.g. would IB allow shorting in such an account knowing they wouldn't have recourse beyond what's in the trust if I go debit)
The broker actually does not impose any restrictions in this case, but there are still some that arise out of tax law.
Qualified plans would have to pay 35% UBTI tax on any "debt-financed" profits, and file appropriate returns. Stock margin is considered debt for this purpose. So you would likely not want to sell stocks short or buy any stocks on margin.
As others have pointed out, this is the same in an IRA.
Another thing is that you should not issue a personal guarantee of the 401(k) account. I was able to get brokers to waive that since it would be improper, but this may depend on a lot of factors including your persuasiveness and the size of the account etc. This should theoretically apply to IRA's also, but is being so widely ignored in the case of IRA's (even IB insists on a personal guarantee) that I do not worry about it for IRA's because the IRS would have to invalidate half the IRA's out there if it were to try to enforce it. But I would not do it for a 401(k).
I should add that although I mentioned the name of one 401(k) plan provider, he may be more conservative (I think he is) in his advice than some of what I indicated.