eg. when building an inline six, there would be an extra slot in the bottom end menu next to the engine block configuration that when clicking on the inline six block would display an additional selection for a slant six,
that could also work for cross plane and flat plane v8s, instead of having two different (possibly four with v angle if that is included) selections for v8s in the engine block menu you would just have one and when that is selected it would display the different possible "sub types"(cross plane, flat plane) in the extra menu
i think it would flow like this:
1. engine block configuration:
2. type (or sub-type):
3. then the usual process after selecting sub-type
Hope that makes sense.