Firstly, don't use Jolteon, as it's heavily outclassed by Raikou, Mega Manectric, Mega Ampharos, and even Magnezone as a Volt Switch user. This is due to Jolteon's frailty and poor movepool compared to other Pokemon. It's also not very strong, at only 110 base Special Attack, which isn't very good in general. Just by getting a feel for your team, I feel as though Rotom-W may be helpful for its additional bulk, Water-typing, and access to Will-O-Wisp. Though as you've said, with walls such as AV Snorlax and Landorus-T, I don't think you need a defensive variant. I'd consider Choice Scarf, as with Trick it can cripple unsuspecting walls and still function effectively.
Definitely run Landorus-T, that thing was literally born for VoltTurn teams, mainly due to its high Speed. Gliscor's best sets don't have room for U-Turn, anyways.
Because Gliscor has to run so much Speed to be effective, Landorus-T tends to take hits better.
Overall, though, I'm not sure AV Snorlax would be a good idea on a Volt Turn team, as well as Charizard Y. I may consider losing these two to add Mega Manectric instead of Rotom-W, and then adding an additional wallbreaker such as Choice Specs Keldeo. That way you'd have three Volt Turn users, a wallbreaker, a late-game cleaner, and then an open spot for something else (Probably a hazard remover such as Choice Scarf Excadrill, as VoltTurn teams tend to despise hazards.)
