So if you bought at $100k and dumped $65k into it and it's now worth $200k, you can only roll over $150k into a new loan--so you're out of pocket on $15k.  

@Stacey AdamsThere is structure known as a Rollover as Business Startup that allows you to basically have your retirement fund invest in your business.The business must be structured as a C Corporation.The business will sponsor a 401l/Profit Sharing PlanYou can rollover your existing retirement savings to the plan.The plan can then purchase shares of the sponsoring company.  

@Tom Hertz The following compares the solo 401(k) and the IRAThe Self-Directed IRA and Solo 401k Similarities Both were created by congress for individuals to save for retirement;Both may be invested in alternative investments such as real estate, precious metals tax liens, promissory notes, private company shares, and stocks and mutual funds, to name a few;Both allow for Roth contributions;Both are subject to prohibited transaction rules;Both are subject to federal taxes at time of distribution;Both allow for checkbook control for placing alternative investments;Both may be invested in annuities;Both are protected from creditors;Both allow for nondeductible contributions;Both are prohibited from investing in assets listed under I.R.C. 408(m); andThe Self-Directed IRA and Solo 401k DifferencesIn order to open a solo 401k, self-employment, whether on a part-time or full-time basis, is required;To open a self-directed IRA, self-employment income is not required;In order to gain IRA checkbook control over the self-directed IRA funds, a limited liability company (IRA LLC)  must be utilized;The solo 401k allows for checkbook control from the onset;The solo 401k allows for personal loan known as a solo 401k loan;It is prohibited to borrow from your IRA;The Solo 401k may be invested in life insurance;The self-directed IRA may not be invested in life insurance;The solo 401k allow for high contribution amounts (for 2015; the solo 401k contribution limit is $53,000, whereas the self-directed IRA contribution limit is $5,500);The solo 401k business owner can serve as trustee of the solo 401k;The self-directed IRA participant/owner may not serve as trustee or custodian of her IRA; instead, a trust company or bank institution is required;When distributions commence from the solo 401k a mandatory 20% of federal taxes must be withheld from each distribution and submitted electronically to the IRS by the 15th of the month following the date of each distribution;Rollovers and/or transfers from IRAs or qualified plans (e.g., former employer 401k) to a solo 401k are not reported on Form 5498, but rather on Form 5500-EZ, but only if the air market value of the solo 401k exceeds $250K as of the end of the plan year (generally 12/31);When funds are rolled over or transferred from an IRA or 401k to a self-directed IRA, the amount deposited into the self-directed IRA is reported on Form 5498 by the receiving self-directed IRA custodian by May of the year following the rollover/transfer.Rollovers (provided the 60 day rollover window is satisfied) from an IRA to a Solo 401k or self-directed IRA are reported on lines 15a and 15b of Form 1040;Pre-tax IRA contributions on reported on line 32 of Form 1040;Pre-tax solo 401k contributions are reported on line 28 of Form 1040;Roth solo 401k funds are subject to RMDs;A Roth 401k may be transferred to a Roth IRA (Note that from a planning perspective, it may be advantageous to transfer Roth Solo 401k funds to a Roth IRA before turning age 70 ½ in order to escape the Roth RMD requirement applicable to Roth 401k contributions including Roth Solo 401k contributions and earnings.)

Assuming that you are able to establish a Solo 401k plan you can transfer your former employer 401k into it (if not you can consider self-directed IRA and rollover your old 401k in there). 

If you can, then sell and roll-over your proceeds before the taxman comes.

I have a SDIRA that is getting ready to rollover and want passive income.

@Robert Smith  Even if you don't want to go SDIRA, I suggest you roll it into a Rollover IRA, not your new employer's 401(k).

In the meantime, I can give you a broad overview...1) You can make an offer now, and at closing the money from your property being sold will just roll over to your new property.2) I believe the identifying 3 properties within 45 days is just to make sure that you are actively looking for properties within the given window.  

@Meg SchlesmanIf you are self-employed and have no full time employees, then yes, you can establish a Solo 401(k) and that new plan can accept a rollover from a prior pension.If the plan is making the down payment, then everything having to do with the property must be under the umbrella of the plan.  

However please note that if you already have Roth IRA - it can't be rollover over into Roth Solo 401k as IRS does not allow this, in such case your only option would be self-directed Roth IRA.Ability to make large contributions to a Solo 401k make this great tax-sheltering vehicle, but the investments you make with either one will not affect your personal taxes because both are considered "qualified retirement plans" and will not have any effect on your personal taxes.