I've been a residential electrical contractor for years, and I'm just now getting into generators and I wanted to pick some brains around here and see how other electricians would go about installing a transfer switch into this scenario in the picture. It's a 400 amp semi-flush, underground fed main panel POCO wiring is in conduit coming up through the cement slab obviously inside the wall, and into the left section of the meter main combo. Surface mount mains are easy and simple, but what method would you use in this application, and how would you do it? What would be the simplest least amount of damage to the area way of doing this? Any help would be appreciated. My thoughts are adding a meter socket box to the left of it, then the ATS to the left of that. My issue is getting in and out of the wall with 400 amps. It's likely 3" conduit coming up for POCO.