If someone fields a Leman Russ at 500... Geez ok try this:
Runepriest 100
Take Hurricane and Lightening . Hurricane will tar pit infantry units in Difficult terrain to slow them down.
Speeder w multi melta 60
5 Grey Hunters w/ Mark, melta, standard 105
5 Grey Hunters w/ standard, melta 90
Your Long Fang unit at 65 points 2 missiles (taking the Squad Leader allows you to shoot missiles at 2 different targets too)
Put them in a Lazorback at 75 keep you priest here for protection. Or just take the Lazorback

Twin linked ...
This gives you 6 major anti tank weapons: the lascannon, 2 melta guns, and the multi melta, and the 2 missiles...
The Russ can only shoot at one....
Only issue here is that there isnt much in terms of Assault or Infantry stability. This is definitely a very strong Tank hunting list though...and that Russ should be gone by Turn 1
To stop large infantry units with this army, use Murderous Hurricane on one of them and shoot your missiles last...that way you can target infantry with Frag missiles if necessary for blasts.