It is certainly possible to make the machine with 600 x 400 mm travels.
It will need to be about 2500-3500 kg in mass in EG/concrete.
X travel:
The problem is 400 mm travel in x vs 600 mm travel is 50% more.
=> 1.5 x 1.5 x 1.5 = 3.3 times less rigid on x.
Y travel:
200 mm vs 400 y, = 2 x 2 x 2 = 8 times less rigid on y.
3.3 x 8 = 27 times less rigid total.