I think you’d have an easier time with the [name_m]Alastair[/name_m] spelling in the US, but either way it’s a great name. The one [name_m]Alasdair[/name_m] I knew during my time in the UK pronounced it with a “d” … [name_m]AL[/name_m]-iss-dare.
I agree with other posters that it’s good to have a few backup options, in case it’s not just cold feet.