tak and wak aren't words but I just wondered if you would pronounce them the same way (if they were) as talk and walk.

I don't know how to pronounce non-words owing to the fact that English spelling is so screwed up. If forced to, I'd pronounce them as tack and whack.

what about talc?

I do pronounce the l in talc, but the vowel is different from the one in talk.

Ceci n'est pas un seing.