I don't have my calipers handy to go measure, but I do know that my Neu 3S 4900's fit easily lengthwise and are at the limits for depth and close enough on height that I don't feel like I need to pad them with foam. They are: 165L x 48W x 26H
The tray is 207mm x 30mm x 42mm. The cover will allow another approx 8mm for a total height of about 50mm. Because of the design however (shape of cover and hinge location) I don't think you'll be able to fit a 30mm x 50mm pack. Also some dremel work may be required to get the battery wires exited properly depending on their assembled config. I really hope someone comes out with a better option.