There is no difference between the old kits and new kits besides the packaging and plans. In fact, the older ones with the blue stripes actually came with pictures on the box but they were glued on and came off over time unlike the newer ones where they were all created on one single label.

How much experience do you have with kit building? Royal kits are not for beginners and require a lot of sanding and carving. They were over engineered and always came in heavy when completed, but once completed, you stand back in awe and admire their scale lines.

I don't believe I've ever seen any Royal kits come with foam parts, however, there are websites that provide vacuumed formed parts for the P-38 to save you time on carving and sanding.

Do a simple search on these forums and you'll get an idea of what to expect from these kits.