In pronouncing "och", can you also say "ock" (so pronouncing a k in the end)?
Yes. The -ck suffix is making the vowel before short, as with every double consonant.
Some examples: hoppa (to jump) titta (to look) kunna (to know)
In Norwegian and Danish, they actually use -kk instead, which makes more sense. "Och" has been pronounced more with a German g back in the days, but is today the only word in Swedish that is spelled with a -ch but pronounced -ck. It's kinda weird that we've kept the spelling, because the word också (also; as well) is spelled with ck and those two words are definitely related.