Drilling Established Aquarium

[byee]

I have a 120g established aquarium currently with a CPR CS102 overflow. Its been running for approximately 3 years. The CPR overflow requires the Lee's Aquarium airlifter to maintain the siphoning action. A pump failure will result in your tank overflowing into your living space !

I'm considering drilling my tank and installing an overflow box from www.glass-holes.com.

I'll definitely need to empty approximately 50% of the water from the tank into buckets.

Here are my questions / concerns:

1] has anyone drilled their own tank
2] or recommend a 'professional' service who can

Thoughts ??