@Steve Vaughan, Understanding that you're in a Deed of Trust/Non-judiciary state, this may be different and as you know, attorneys would prescribe different methods of doing this.
But the whole reason why a Warranty Deed was not given by the seller is due to the fact that doing this way will defer the taxes that the seller had to pay. Such as Capital Gains. The seller would have had a huge capital gains bill. After consulting with an Accountant and our attorney, the best thing for the seller to do was the keep the Warrany Deed on an escrow until we (a) pay off the seller completely or early (b) financing the remaining balance out through a bank. If the deed was transferred, the seller may had to pay the capital gains all up front. Plus, it gave security to the seller knowing that if and when we default, the seller wouldn't have to "pull a tooth" to get the deed back.
The contract stipulates basically everything as far as keeping the title clean or otherwise we can sue for performance. It also stipulates code violations, the terms for early payments, what constitutes default, etc. I can send you a copy of our contract template if you'd like to see what's on there.
When we do go get financing on this from a bank or another formal institution, it's actually considered a purchase loan but... by the time we do this, we may only need to do 45-55% LTV since we paid the majority off through the installments. As you can imagine, banks would see this as a less risk profile in terms of underwriting.