I have similar fitness, based on your hr data I would recommend you to slow down more at AM session 5x6min on treadmill till HRavg below 145 at least.
I am running now on treadmill (job at sea), just now did continuos tempo 40min @MP pace, and my HRavg only 146, my max HR=183.
Once you get lactate device, you will be surprised how slow you should perform double threshold sessions compare to your earlier feelings without device...
Good recommendation, especially for "treadmillers" doing double threshold programm I found like this:
Tuesday:
AM session: 5x6min/1min rest at pace threshold speed minus 1 km/h
PM session: 20x400m/30s rest at pace threshold+0.5 km/h, if feeling good, last reps at pace threshold +1km/h
Thursday:
AM session: same as Tuesday
PM session: 10x3 min (8 reps if feeling bad, 12 reps if feeling good) at pace threshold speed.
Also there is a variation:
Tuesday PM session move to Thursday PM, so there is a choice: start week with the fastest double threshold and end of the week finish with slower one, or vice versa.
Saturday: here should be "X element" session.
Keep in touch, as I want to include in my marathon preparation starting from next week "6 weeks block with double threshold all weeks on treadmill including X element as a hill workout", my avg weekly mileage now is approaching 100 miles