A subsea well assembly has a tubing hanger that lands and seals in a wellhead housing. A tree block is lowered through the drilling riser into engagement with the tubing hanger. The tree block has a lower portion that inserts and latches into the bore of the wellhead housing. The drilling riser is disconnected, and a module is lowered onto the tree block, the module having a choke and controls for controlling the well. The master valve for production is the downhole safety valve in the tubing. The wing production valve is a ball valve located in the flow passage of the tree block.