[ref]NW1[/ref], unfortunately it seems you're getting a lot of UK-based advice, but the principles remain the same.
Assuming this is the car you are looking to drive 650 miles home in then I would suggest you confirm that there is someone near to where you pick it up that can both fit tyres and align the car.
If you get new tyres fitted and drive 650 miles on them with alignment that is incorrect you could easily scrub them out on the edges.
In that case you'd be better to drive home on the old tyres if they are safe to do so.
Having said that, if the old tyres show no signs of uneven wear then it is likely that the alignment is more or less correct anyway.