Power up snorlax with L/BS or ZH/BS?

If candy really doesn't matter then zen headbutt. It will do more damage and have higher energy gain then lick on defense vs any attacker. Good luck catching/hatching all the snorlax required to hit that though he is a rare spawn/hatch.

ZH/BS because it makes a better defender...although the L/BS will have a higher CP if they are they same level.

That said, if dust and candy are not an issue then I say both.

Zen Headbutt, because it does more than twice as much damage as Lick (three times as much on Fighting mon). Though I personally think both of these are far too low IV to be powered up (if the ZH Snorlax was also 71%, I'd say definitely go for it, but 55% hurts)

I would power up the L/BS one.

1. Even though ZH/BS is the better defensive MS of the two. But a gym attacker does not know the ms of the mon he/she is attacking so it's not a deterrent. Also, if an attacker is committed, he/she won't care what ms your mon has.
2. The L/BS Lax will have higher CP due to higher IV. I know the difference in CP won't be much, but it matters still becuz it'll affect your placement in gyms. Higher CP means your Lax will potentially hold a higher spot. With gym placement determines only by CP, the higher the better.

Aparently, your question is only about the moveset for a defending Snorlax as you don't care about dust & candy and you just want you mon to reach ~3000CP. So it's surely the ZH/BS one.
Otherwise, the L/BS one will be the choice as it costs less dust and candy now and it will have higher CP at the end. Moreover, at high CP, let's say 3200-3300CP, a L/BS and a ZH/BS will have little difference as most of its damage will come from BodySlam moves.

It's unlikely that their performance will be that much different from each other, as Body Slam is the most important part here. So, the answer is actually both, starting with the one that costs less to reach the target.

ZH is better for defense
Lick is better for offense because cane be spammed

but in defense the AI use your pokemon not you, so you can spam it it will be used by intervals, and ZH deals more damage in the end plus hits harder in counters like machamp actually hits harder than lick vs anything in the end because lick damage is so low, it need to be spammed for be good energy/damage quick move

Just wanna note that Body Slam is by far the best move for a defending Snorlax, and it is now a legacy move, so the suggestion to wait to get a better Snorlax seems kinda moot.