Unfortunately GW is 28-32mm...actually, I don't think they know what they are

.
One thing to watch out for, that I have learned from trying to use historical kits (trying to find suspension for Guard tanks), is that even within the 1:42 scale some stuff matches up to 40K perfectly, other stuff is tiny in comparison, and other stuff is massive. Weapons are the most notorious for this - I've a box of machine guns that I thought would be useful as Stubbers, and the barrels are thinner than a Guardsman's eyeball.