340 coolant temperature

Check your lower rad hose to see if its collapsing when the rpm is increased impeding flow? Something fast to check with a buddy. Also check if its got a spring initmor not while your at it.

I'd also address why the fans come on at ignition and stay on. They should thermostatically controlled to come on at a certain temp or manual controlled with a switch. If they are on all the time and the car is reaching 160 operating temp at idle the your stat is working ok.

Good luck! That's a nice rad and fan set up. Wonder if the prev owner had the same issue and threw that monster at the problem hoping it would cure it via shotgun method. You'll get it sorted. Seems to be a flow related issue to me.

Good luck!