Check Reveals -v- Insulation -v- New Windows

[Fraser Lamont]

Hi, I'm currently renovating a house on Skye, typically in Scotland, the window recesses have check reveals. I'm looking at getting Nordan Alu-Clad Windows. Problem - there are check reveals. I want to get rid of the old timber in the recesses, the house built mid 70's I think the original Windows (long gone) attempted  (badly) to close the cavities. I want to install the new windows the way the house was originally built - front face of window frame tight up to inner face of external block leaf. Problem would arise where window fixing straps/brackets are used. They'd either have to be bent a lot to reach the checked reveal thereby making it difficult to install Insulation on the reveal, or could I pack out the inner reveal with something like compacfoam and fix the brackets/straps through that and into the edge of the inner block leaf. We get some wild weather now an then so like the Windows to be recessed nicely. If I can use something like compacfoam, could I continue it into the Cavity to the inner face of the outer block leaf in order to close the cavity? Or do I make a timber frame to fit the inner block leaf window recess, fix that into the reveal then fix Windows to that? So many different ways of doing this, I'd really appreciate input as to what's the best course of action. TIA