As far as I know, there isn’t any set of pairs of usable hash functions for each two altcoins. Nonetheless, before you dive in, you need to make sure that the altcoin is tx-malleability-free or that it has BIP65 deployed. If you are interested, I have an optimised script you might use.

Be prepared to run into many hurdles if you’re going to implement this kind of exchange from scratch yourself (I mean, the script is the least issue and you can use an already invented one—but there is much more around it that you need to take care of).