It is true the Junta did set up an oil fund.
This would be a disaster for pro-union groups. Scotland has about 90% of the oil reserves in the UK. If you have a large fund, getting larger every year, shared across the UK but 90% of the revenue is coming from Scotland, that's going to make things very difficult for Westminster. In OTL London could obfuscate as to how much the North Sea was bringing in, but with a separate dedicated oil fund? It's much harder to hide.
And what happens if Scotland does become independent ITTL and sues the UK government for 90% of the sovereign wealth fund? A sovereign wealth fund would be a disaster for the UK because unlike Norway the UK has a lot more internal divisions and I think the planners in Whitehall would know this. Esp if there is an armed struggle in Scotland at the time when decisions are being made!
Could I recommend retconning this and instead having the junta use the income from oil and gas to make up for the diminished access to world trade as a result of lack of membership of the common market and embargos? You could also say that some of it was allocated towards increased defence and security expenditure.
Edit: I loved the update! The world you're building is fascinating.