I would like to know if anyone tried to use GT (GT-S) struts on ST (GT/ST). I'm not crazy let me explain and ask two questions:

for US/CND members
Do GT-S struts (those called "sport package") fit on common GT or ST?

for European members
Do 2.0 GT struts fit an 1.8 ST?

note: US/CND GT-S struts = Euro GT struts and US GT/ST struts = Euro ST struts . I just need to know if there is any difference on size, bolt spacing, etc...

Yes they do!

When I fitted my Tein Coilovers, my old Apex -35mm springs+stock shocks went on the ST Celica owner who helped me fitting my tein's. Straight swap, everything lines up. The only difference really is the front spring which is stronger for the GT, because of the heavier engine I presume.

for US, the ST and GT struts are the same. The only difference is that the "sport suspension" ones have a sealed strut in the front, as opposed to a strut held in by a big nut.

You can swap the strut housings no problem with GT/ST.