You’re asking for problems here.
If you don’t have the personal information on the original borrower, such as SS #'s, birthplace and maiden name, along with online access codes, you will have an impossible time if you need any loan information, payoff amounts, escrow disbursement questions, insurance/tax impounds, or other customer service issues.
You would effectively assume “responsibility for the loan” even if not technically speaking. It’s up to you to maintain the loan, handle liens issues, etc.
If the house has any liens, other than the mortgage, this would be an issue the seller has to worry about …in order to give you a marketable title (subject to the existing loan(s)).
Meantime, the seller has no liability to the loan, since he’s not the original borrower.
If the house is refinanced or the loan is paid off before the house is finally sold, the lender is required to record a lien satisfaction notice. So, there should be no problems regarding the payoff of the lien.
However, you need to know if the original borrower is still depreciating this asset, or not, or taking a mortgage interest deduction. This makes difference if you want to do the same thing with the same property while you own it (or if you seller finance it to someone else).
Land Trusts do not alter liability for a loan, one way or the other. It’s mainly a tool used to provide privacy.
Get the original borrower’s information so that you can elegantly and efficiently deal with the mechanics of the loan.