[blacknife]

i have never had one but i believe those HOB overflows will not over siphon the tank. the part in the tank is a small overflow box and when the water is to low no more will drain. some use a qualifier pump to regain the siphon if that low water condition breaks the siphon.

drill bits are cheap it would be easy to find a non drilled .. or even already drilled tank. diy it to the specs you need, and then move everything over.

or depending on what you have going on for a tank just put everything in a rubbermaid holding container, do the work to your tank, rebuild everything, get it running then move the livestock over when everything is kosher.

if the available ones are to expensive you could probably diy one that is just as functional for fairly cheap if you are at all crafty and can do a good google search.