When the land trust is used in a Pactrust or any subject too situation the original owner is the owner of the beneficial interest. The investor then assigns the interest to themselves. In the case of the Pactrust a residual interest is left with the owner. They pay or may not participate in future proceeds. The majority interest controls the trust. Like many other investments you can also control voting rights but not the investment proceeds. Title always resides with the trustee no matter who the beneficiaries are.
When you take title, even if you pay cash, you do so with the land trust so that your name does not appear in public records. If you have a contract to buy at a date in the future so that you do not go on title then, yes, you can assign to the new buyer. If you are worried about the deal being upset when the buyer finds out how much you are making then you would do a simultaneous close and do the title with the trustee of a land trust.
A Pactrust starts with a land trust. I use a land trust for anything that I will title. There is no use informing anyone what I buy or sell. If it is going to be a flip and you do not have to take title then assign the contract.