If it is a separate casting then firstly ask the supplier if they have a revised drawing.
If that fails then you have two options.
1. Cap head screws up from below with counterbored holes in the underside of the saddle
2. Just silver silder the two together and treat as one.
3 if the castings are not that good and as all surfaces will need machining, start with a block of metal and replicate the single casting with integral saddle.