Securities based loan

I've just found out about something called a securities based loan and am wondering: Once a transaction like this goes through and one owns the property, can you refinance, using the property as collateral instead of the portfolio of securities? Would a loan like this amount to a cash deal for the seller? Is there a limit to how much of one's portfolio one can use for this purpose? I was thinking of getting the loan based on 70% of the current value of the investments and only using 50% of that loan to buy the place. That would allow for market fluctuations. There are okay studios on the market for $500,000. Any thoughts?