Not that kinda freezing!, some metals have a way of bonding. ALu & Steel do. copper grease can prevent them 'sticking' together. have you never considered using a chiller for the water?, you'd have to lag the block then. what kind of 'modifications' were you thinking of?.
What kinda case you got?, you can fit the (TEC)lot in a midi you know?.a TEC PSU will fit in a CD~ROM bay. it's always good to leave an avenue open regardless.
PS, it's best to say TEC like I do if you can't spell Peltier
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