Modifications to Offenhauser 1 1/2 carb spacer Thermoquad to Holley pattern ?

For what it’s worth, the intake manifold you have for sale is a much better choice for what you are doing than what you are trying to use. Again, not trying to pee in your cereal this morning, I just hate to see the the results with where you are headed.
The manifold that is sold is LA, no holes for magnum, must drill the magnum heads