Awesome. I think I have my marching orders.
I will carry on my initial estimated Z2 6 days/ 1hour per week until my heart rate is happy and stable and then do a ramp test and reset numbers.
I then plan 4 days /1 hour at Z2, a single day for a longer Z2 ride, a rest day and add a day of SS/Tempo intervals. I plan to ramp the time at intensity of that single day of intervals over 6 weeks as appears attainable and then retest.
Your collective wisdom much appreciated,
I better go get on the trainer.
PS. Isn't nice when someone says senior and not older. I still get confused when some young nipper calls me Sir.