What is the process for registering a motorcycle at the DLT in Thailand, and what documents are required?

Does not matter which visa it is the same. You need a Residence Certificate and the details should state it is specifically for that reason ie vehicle transfer. The seller will give you the Green Book and Bill of Sale. Take copies of your passport and the documents above to the Department of Land Transport along with the vehicle. It is completed there and I think the cost is circa 500 THB (you can scan the money but it costs 10 THB cash too for some reason). I just registered a bike last week and I am pretty certain that is all that was needed - it worked anyway. There are usually agents close to DLT offices that will do it for you for a few hundred Baht. It does smooth the process. As with anything in Thailand how easy the process is often depends on which particular office you attend. My friend has a pretty large garage selling mostly cars and some bikes. There are certain DLT's she avoids.