You can always mill out your spread bore intake to accept a square bore carb, as the Edelbrock carb will accept the spreadbore bolt pattern, very simple operation for a machinist I have seen it done a bunch to cure the problem you have encountered, and done a ton on early hemi original intakes (they where originally spread bores), I had it done once years ago for $25, it was cheaper than the adapter, you just have to pull the intake.