update!!2004 taurus engine had correct 4 releif piston,the heads are different only where the water pump is driven and valve cover bolt holes.Both sets were roller follower rather than buckets and all internals are the same valves,springs,guides, locks and seals.it appears the chains and tensioners are the same and of course the rails,cams and gears are different.I have not yet assembled the engine back as i have had a hard time locating the o'rings for timing housing into the vvt and for the head.Mazda could not even look them up.I ordered some for a 07 ford fusion and they were extremely expensive 19.45 per ring(6 needed) and they could not service the housing seal to head(2 needed).i decided to look at jaguar and they serviced both part number large o'ring c2c8281 $.89 each and part number c2c8278 small o'ring $1.45 each for a grand total $8.30.i hope they are right when they come in i have my fingers crossed.