Is there a way to use a self-directed IRA to purchase real estate I already own?

I know basic information on Self directed IRA's.

@Laura KastnerAs a plan provider, I cannot make a specific recommendation as to a company to work with per BP guidelines.Several firms that specialize in self-directed IRA and Solo 401(k) plans are active here on Bigger Pockets.  

However, I am having a heck of a time trying to figure out how to transfer my 403b to an IRA. 

If a limited partner  investor invest money out of his self directed IRA will he get hit by UBTI? 

I have about 50k sitting in a IRA. it was a old 401k that I rolled over.

I have been saving $$, self-directing my IRA account, investing in stock options, completed the real estate salesperson course, and became a Pro member of Bigger Pockets.

My question is should I convert the previous 3 401ks to self directed IRA or just transfer them to my new employer and eventually just borrow 401k from them? 

At age 32, I have over $400K of investments with zero debt, but have yet not invested in anything outside of a Roth TSP, Roth IRA, and mutual funds. 

@Chris StrattonYes, it is possible to finance a purchase of an investment property in your SD IRA LLC.