Really could use some pics, especially of those 'beefy' fans. Many fans for servers aren't standard case fans, they'll have a 6pin connector and can even look like 2 fans back to back or 2 fans that look like they are opposite. Servers have limited space usually, so often end up with extreme high static pressure fans, that run extreme high rpm, Delta server fans can top 8000 rpm and sound like a miniature jet engine in takeoff.
So before any case modding, might want to see if the fans are actually usable, and livable.
IF the fans are compatible, chances are the only place that'll handle a 180mm fan is the side panel. If anything I'd mount that there and run it at low rpm, under 500ish. That will move plenty of air into the case without totally blowing out the airflow stream. The 120mm I'd stick low front at higher rpm, 700+, and use it to move the block of air from the 180mm under the gpu. The 90/92mm I'd stick right up next to the other case exhaust, possibly at the top rear as supplementary exhaust, create a larger low pressure spot in that corner, help the intake air move in that direction.