Your 3U looks like a PlinkUSA Design.
Ive got a 4U side to side for an 8086k rig they make.
Its their side to side cooled 1U I would use if I go with a 570 design.
A 470 design would be easier as Id swap out one of my 1U Supermicros.
Ive got a rehearsal rig, a spare rig and the 4790k rig I just built using NOS parts I bought 6 years ago.
Ive got finicky drivers so when something works I stock up.
PlinkUSA has excellent chassis though, you're fine with anything they make.
The 4U below is a great outdoor rig.
Just throw a Noctua Cooler and a pair of 120mm for the sides and you can suck a marble through a hose.