Individual 401K - Buy/Sell Land - Conflicting Info

[Jim Froehlich]

I have an existing 401K that I am considering rolling into a solo-401K for single-member LLC side business I have. The brokerage it is with tells me that I am not allowed to invest directly into real estate or notes - however, third party providers of solo-401K set-ups are telling me that if I set up this with them, I will be given a free brokerage account (with this same company) with ability (via checkbook) to invest in real estate, notes, liens, stocks, etc. Which is correct? Also, if I use that to buy/sell land in less than year increments, my understanding is that since such transactions are treated as ordinary income, then it is earned income and can be placed back into the 401K. Sound right?

[Jim Froehlich]

@Justin Windham, @Dmitriy Fomichenko, and @George Blower.  Thanks for the incredible feedback!