Tips to tunning up to a 1000km ultra event in early June

So, I have around 9/10 weeks before this event and I’m a bit clueless on how to proceed from now on.

First, the context, I’ve already done this event two times in the last two years and I regularly do 200/300km rides. Last week I did an event that was 312km (200 miles) and 7000 meters (23000 feet) of elevation in under 20h so I’m used to long distances.

The thing is, I’ve been doing some “structured” train averaging 400/500TSS a week (between 8h to 11h), on a pyramidal philosophy, but I know that it is probably sub optimal and I wanted some guidance on what to focus from now on.

I think I should push for more volume, because that’s what I will be doing in my event, but I don’t know how to do 10h to 15h a week with high intensity intervals in the mix. I probably could do the intervals in the first week but I doubt I could do it on the second.

I don’t want to dial back to 7h a week so close to the event just to be able to handle the high intensity ones.

Regarding Z3, Z4 and sweet spot, what and how should I be doing?

I’m kind of lost at the moment