KRV,
Look forward to your build. I made a decision ages ago to only use Metric fasteners. Not that I have built any bought casting models but certainly modified a few imperial drawings to metric.
I notice that you have BA bolts provided with the castings so perhaps use them as it would seem no tapping on your part is needed.
At least in my tiny shop using metric I do not have to keep multiple supplies of fasteners, drills, taps and dies. Will not suit the purists but I build stuff for my enjoyment and sometimes frustration. Either way I learn stuff, even if it is not to do something that way again.
God luck with your build.
John B