I think KV-8 should start with less pen for the gun but gain the current values at vet 2 or vet 3. This gives the German player some time to react and develop counters to KV-8 (like Panther) while their T3 can somewhat hold a stock KV-8 back. If the threat is ignored and the KV-8 is allowed to vet up, it should then be very dangerous to deal with using only ATG and T3.
Heavy infantry tanks have a role (to absorb damage) and their veterancy should help achieve that role. KV-8 should have armor/HP/armor reduction as veterancy buffs.
The whole approach to KV-8 changes is simply wrong. The unit should serve as shock unit that loses value in late game. It should not serve as a counter to PzIV4 for a number of reason.
Since it specialized unit it should be cheaper and come earlier than KV-1.
Change from live could include:
Veterancy overhaul focusing in defensive bonus, vet 1 ability could become a timed damage reduction, lower rear armor, small increase to gun's penetration.
Unit available as call-in at normal price and build-able from T4 at cost discount to 110-120 fuel.
As most flame vehicles DOT damage should be decreased or even completely removed and added as timed ability, normal damage might need re-balancing.