Hey,
Pretty cool balance team and spectacular art; I'll do my best to help you out! I'd start out with Celebi -- you have a good VoltTurn core and already have a good VoltTurn combatant in Latias, so I see no need to use Celebi on the team, especially if it aggravates a Pursuit weakness. You've wanted to use
Heatran, and it seems like a pretty good replacement. A speedy Air Balloon variant should suit you fine, and it maintains offensive pressure while beating down Dragons locked into Outrage. With that in mind, your defensive core seems solid, as Gliscor, Heatran, and Latias can cover most of the major threats in the metagame. While I would suggest running Substitute on Gliscor over Taunt, you have no spinner, and there is simply not enough room on the team for one, so Taunt should suit you fine. Just make sure that if you happen to be matched up against a Rock Gem Terrakion, you won't lose your method of beating it, Gliscor.
You seem content with your Scizor set, so I wouldn't say this is a mandatory change. However, in my opinion, you would benefit a lot from a Swords Dance variant with U-turn and Roost. With U-turn, you can retain momentum and bluff a Choice Band set even better, and with Roost, once you have revealed you are not a Choice Band variant, you can heal up and do even more damage later. I've had a lot of success with this variant and it seems as though you should be able to pull it off. Besides, Air Balloon Heatran is the perfect switch-in for Magnezone and opposing Heatran, so with U-turn and Heatran you have those covered fine (though Choice-locked Magnezone will require a bit of prediction to play around).
Finally, if you ever find yourself being eaten by hazards, you can always opt for Starmie over the Heatran I just mentioned. While it doesn't seem as though it's too big of a problem, VoltTurn typically enjoys having hazards off the field, and this also makes walling a hell of a lot easier.
sets
Heatran @ Air Balloon
Trait: Flash Fire
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature (+Spe, -Atk)
- Fire Blast
- Earth Power
- Hidden Power Ice
- Toxic
the next two are more of optional changes, but I included them just in case you wanted to try them out
Scizor @ Iron Plate
Trait: Technician
EVs: 248 HP / 100 Atk / 160 SpD
Adamant Nature (+Atk, -SpA)
- Swords Dance
- Roost
- Bullet Punch
- U-turn
Starmie @ Leftovers
Trait: Natural Cure
EVs: 248 HP / 36 SpA / 224 Spe
Timid Nature (+Spe, -Atk)
- Rapid Spin
- Scald
- Psyshock
- Recover
Cool team, and good luck. I hope I helped!