A good, reliable, all round heavy support layout I often run goes something like this:
Leman Russ Squadron
+ - Leman Russ Battle Tank
- Heavy bolter
- Pair of Heavy bolters
- - - > 170
Leman Russ Squadron
+ - Leman Russ Battle Tank
- Heavy bolter
- Pair of Heavy bolters
- - - > 170
Manticore Rocket Launcher
- Heavy flamer
- - - > 160
500 points total, for plenty of S8-10 pie plates and 18 HB shots. You could save 40 points by not taking the sponsons for the Russes, I'd always, always take them though.
The only downside is you have some trouble cracking open heavyweights like Land Raiders at range, although the Manticore can get lucky.
For that, sprinkle some Lascannons into your infantry squads (not paired with a special, LasCannon is expensive enough and has poor synergy with most other weapons), get a Vendetta or two, or try out the Devildog with additional Multimelta. If you want to sped more on HS, swap one of the 'nilla Russes out for a Demolisher. Pimp up to taste.