1/350 People

hmmmmm not sure myself.

Test with a few.....  take a few photos in various areas of the ship.....   objectively examine them....  ask your friends....         You might be able to make it work

best of luck with it

Using 1:350 scale figures on a 1:400 scale model will have them looking about 12% too tall.

Example - say a figure represents a six foot person (72 inches).    Using  1:350 scale figures on 1:400 model would have them appear to be 81 inches (6'9").     They may appear to be too tall.  While one or two tall figures may be fine - everyone being that tall might not look right

My personal preference is to not mix scales where the difference exceeds 10%.    The difference is just too visually jarring

I mixed 1:450 and 1:500 people on a diorama, but that is a bit less of a difference than 1:350 and 1:400.  Still, I found the mix fine- did not really notice the difference.  One of the sets I used had a number of children, so that helped- you could see a mix of sizes anyway.

A thought- you might want to consider the 1:450 people. I believe I got them from a Japanese importer- there is a new micro size model railroad scale at 1:450 and accessories include people and cars.  These are civilian people, though, but you could probably just repaint adult males.