I am trying to buy a house with a 426 FICO score

I have a question for you and hope that you can help me. I am trying to buy a house. My credit is awful. My FICO score is 426. I am trying to get a letter of pre-approval or something from my lender. Because of my credit score the sellers are allowing me 6 months to get my score cleaned up enough to put the house in a loan with my name. They are letting me do a lease purchase for the 6 months. I already have things in dispute with the credit bureau and I am waiting on them to contact me back. Is there anywhere possible that I can try to obtain a letter of pre-approval or something?
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pre approval?
for a 426?
no I haven't. Letter?
you need owner financing.
3 open rated lines of credit 12 months MR
and obviously you have nothing but a slew of bad credit. some of that need to go away