LS Cooling Issue

[MotoWells]

Just completed an LS 6.2 swap in my 71 GMC

Unfortunately, I'm having cooling issues. I was hoping to get your thoughts on my setup.

I have a large capacity radiator with overflow and dual fans that seem to kick on ~200 deg. For now I am just using distilled water and a little coolant. Just started to run long enough to get an initial road test. On my recent road test the temp bounced from 180 all the way as high as 240 maybe even 260 and would not fall off while driving. This is obviously way too hot, dual fans come on etc. I suspect from reading other posts this could be due to an air pocket and that I need to "burp".

I also wanted to post some pictures of my setup in case something looks odd. Additional possible concerns - (overflow is to low, steam port is to low, steam port is introducing air, heater core has introduced air, wired dual fans with pigtail directly to GMPP controller cfan output)

Filled coolant through radiator not through engine hose. Never opened up heater until yesterday when heat started to climb.

Thanks for any thoughts or comments.