Thoughts on replacing existing timber legs with concrete blocks

[Space Race]

We have a 10x5m log cabin that's raised off the ground on (sleeper type) timber posts. These posts are now at varying stages of rot and I'd like to replace them with something a little hardier. As a side note I'm also looking to insulate and clad externally so these new supports will project out 100-150mm around the perimeter. The ground level slopes and the attached drawing shows the gable end where the ground is at it's highest with only 110mm clearance. On the opposite gable (not shown) the grounds much lower with a 450mm clearance. 

 

It's tricky as I'll need to prop the frame (possibly jack, depending), Remove the rotten leg and small pad its sat on, then dig the new foundations in the tight space between floor joists. I'd only be able to do a few holes at a time due to the propping and if I fill each hole with concrete I've a further wait before being able to build off it.

 

I was thinking about using hollow concrete block stacked on top of each other in the hole with concrete poured both into the hole as well a inside the block itself, more to tie them together than anything. This means I could get the new support done in one hit but the bottom block would only be encased in concrete, not sat on it. 

 

Has anyone any thoughts on this? Feel like I'm too close to this now with overthinking and unable to see the woods for the trees

SH_Gable Foundations RHS.pdf