Hydraulic lifter part numbers are different too between early and late 3.2s, apparently not interchangeable between lumps? 
The none ecentric bottom roller went to all models, it was intended to reduce the belt noise which is common with this engine but didnt work, you can still fit the ecentric roller- the later tappets had a none return valve fitted - you can swap them to older models aslong as you fit the later T vent which has larger oil hole in it.
the idea of the later improved tappet was to solve the problem of tappet noise on start up - those few seconds of tap you get with the older design - you can identify the different tappets by comparing the underneath view.
you can get tappet bore wear though where even new tappets will not improve the noise - if your old tappets have score marks on the sides even new tappets will not improve the noise level - we put this down to casting sand retained in the head - at one point we went to Cosworth to supply heads - they used the Cosworth process that turned the mould during the casting process which reduced blow holes - unfortunetly they also used a different casting sand - this reduced tool life dramatically on the machining lines plus they couldnt keep up with supply so they were binned!