OK I'm going to make a unconventional suggestion.
I think Flamethrower should be slashed on SpDef Heatran with Lava Plume. I also think 248 HP / 16 SpA / 244 SpDef, Modest should be considered as a spread. With that spread and Flamethrower, you increase your damage output by 57% at little cost to Heatran's effectiveness.
SpDef Heatran lacks any kind of power and hits like a fucking pussy. Flamethrower keeps your opponent honest in that regard. Lava Plume isn't usually better than Flamethrower because Heatran is running Toxic / Will-O-Wisp anyway (sometimes both). Tyranitar, Garchomp, Terrakion, Tentacruel are the only targets you really want to burn. You actually are better off using Toxic on Bulky Waters and Latias. These pokemon all take a pittance from Lava Plume anyway so you are better off going for the status on the switch as it is.
Again, not saying Flamethrower is completely better but they should be slashed. Special Defensive Heatran doesn't make most teams break a sweat and is horribly underwhelming. Fuck, I set up spikes with Ferrothorn (in rain) on it before. It doesn't OHKO Bulky Scizor in the rain either, LOL (have fun eating a +2 Superpower to the face).
ImStillGood (Salamence) (M) @ Life Orb
EVs: 252 SAtk / 252 Spd
Rash Nature (+SAtk, -SDef)
Draco Meteor / Flamethrower / Brick Break / Roost