I honestly dont think 6-8 weeks is enough, whether polarised training or not , to approach a multi day, long rides with loads of climbing event. It simply doesnt give you enought time to improve your endurance fitness. With a 2 week on/1 week off plan you are looking at only 4-6 weeks of actual riding. Life intervenes in our best laid training plans and you would be unlikley to get the most out of such a short period without illness, work/life stress getting in the way. No dout there would be some tangiable improvement but i doubt of the level required to have a meaningful impact on endurence, especuially over 5 days of hard riding. That said Andy, you are welcome to join us
Id be riding 5 days a week of varying duration, virtually all Z1/2. For 6 weeks. I would do 3 weeks on increasing load then 50% of that on week 4 then repeat.
As Alex alluded to, it's the starting base line, which is important.
The longest turbo session I did to get ready for Tenerife was 2.5 hours. Has you know Bob an indoor turbo session with literally non stop pedaling is far superior in training than an outdoor 2.5 hour session.
I found the week very pleasant, no difficulty.
What was the biggest game changer for me was cutting out virtually all carbs. I became fat adapted, needed far less food and only drank water on ride days.
I understand your reasoning, but you're coming back after a period of non riding from surgery.
My year off from cycling, took me 4 months to get 80% maybe a bit more to feel fit again