Contract Sale Questions

[Kent Braaksma]

I own a vacant rental property that I am looking to sell. I have an interested buyer, but they want contract terms. I have a current mortgage on this property totaling aprox. 23k. The purchase price will be 60k.  I am thinking 10% down, with an interest rate of 8.5% (depending on credit report) for a 10 year term. 

This seems like a really straight forward contract sale, but don't know if I am in-line with interest rate. Also, can I sell this property on contract without paying off the current mortgage? I would double the payment made on the current mortgage to about $400/month, but would receive $668/month on the contract. 

Am I dreaming here?