The import and ToT were of the same Israeli round. You are correct that HAPP Trichy manufactures 120, 125 and 105 mm FSAPDS rounds.
Mk2 was supposed to bring advances from the Arjun round to the 125 mm round. It is supposed to be even better than the Israeli round. I am using the word “supposed”, because I don’t know how well the round performed in the field.
I am a sailor and clueless on the Russian rounds. My good friend referred ammunition only as Russian, Indian and Israeli. I doubt it whether he too knows the specific designation. These chaps arent too good with nomenclature.
I agree on the 'informed' bit. Keeping my dad as an example, my observation is that defence personnel tend to be very focussed on things they do or are supposed to do. But their GK about other matters related to military is pretty limited. My dad for sure won't be able to differentiate between T-55 and T-72. It is left to fanboys like us to troll the net/read up on literature and think of ourselves as arm-chair generals.
That apart, the real problem is the auto-loader on the T-90. The absolute limit of round is 700mm. The projectile will be lesser in length than these. I don't know wether the our T-90 came with 'modified' auto-loader, for there is a russian APFSDS with 740mm round length.