I've tested Pre-evolution Stone.
I used this Pokémon for attacking: Starmie, 31/31 IVs, 128 Atk/128 Sp. Atk (I know it's a bad EV spread, but it's fine for testing).
My defenders had max IVs and no defensive EVs.
Ice Beam vs. Porygon2:
195 Sp. Def (normal): 94 - 111
292 Sp. Def (x1.5): 63 - 75
Actual damage: 69, 68, 70, 72, 68, 73, 64, 70, 67
Ice Beam vs. Porygon:
155 Sp. Def (normal): 118 - 139 damage
232 Sp. Def (x1.5): 79 - 94 damage
Actual damage: 86, 79, 94
Rapid Spin vs. Gligar:
246 Def (normal): 13 - 16 damage
369 Def (x1.5): 9 - 11 damage
Actual damage: 10, 9, 9, 10, 11
Ice Beam vs. Munchlax:
175 Sp. Def (normal): 105 - 124 damage
262 Sp. Def (x1.5): 70 - 83 damage
Actual damage: 79, 73, 73
Rapid Spin vs. Munchlax:
116 Def (normal): 28 - 33 damage
174 Def (x1.5) 19 - 23 damage
Actual damage: 22, 21
So it seems to boost the Def and Sp. Def by 1.5 times for any NFE Pokémon. I tested with Dunsparce, a fully-evolved Pokémon, and it did the normal damage (didn't record it, though).