From what I can gather, the first engines were built by Mountune for Ford in 1998 and they were an unlinered CGI block and ran Mahle pistons and rods with their inlet manifold.
In the mean time, Ford bought Cosworth and moved the operation in house in late 1999. They need more power, torque and reliability so started from scratch with the engine, although the cross over period of 2000 the engines remained very similar with a Mountune still supplying parts.
Cosworth then machined all the blocks, linered them with their own pistons, rods and crank and later revised the inlet manifold. Then other various changes came through as the program went on.