A.
The answer is “No”. There is no size limit.

As written in DGR 6.2.10.3 the maximum net weight of UN Packaging 4D Plywood Box is 400 kg. The definition of LARGE PACKAGING shown in DGR Appendix “A” Glossary reads: “Large Packagings are packagings consisting of an outer packaging which contains articles or inner packagings and which are designed for mechanical handling and exceed 400 kg net mass or 450 L net capacity but have a volume not more than 3,000 L.” It describes a large packaging containing articles in excess of 400 kg, thereore the size limit of 3,000 L do not apply to UN packaging 4D which is limited to 400 kg net. The size of the 4D Plywood Box is not regulated but it must obviously be of a size strong enough to hold net 400 kg .

You will notice that throughout DGR 6.2 the maximum permitted net quantity for solids is 400 kg or less and the maximum net quantity of liquids is 450 L or less. Their sizes are not regulated.