While Heavy Slam isn't Body Slam it is still quite good on defense. I've fought against a few and it still comes pretty quick and hits decently hard for a multi-bar charge move.
I have an 89% ZH/HS snorlax I hatched and I plan to power him up next. I'm currently walking him. I think you will be happy with a 93% maxed out ZH/HS Snorlax.
Having said that I also might power up your 71% Lick/BS snorlax to about 3000CP. While Lick isn't as good on defense as ZH the Body Slam is still a killer. and a 3000CP BS Snorlax will still be a pain in the butt. And it is already so close to 3000CP.
Eventually if I were you I would aim at having your B, C and D options at around 3000CP. All will be good defenders. Just depends on your priority.
Powering up D and then C options would be quicker and get to use them a lot sooner depending on your candy situation.