Does this program solve the issue of converting images to the ROM?: http://devster.monkeeh.com/sega/imagenesis/#introSaying this because I saw some cool super transformation sprites on Twitter...
I've actually found an even better compressor/decompressor over at https://github.com/temisu/ancient_format_decompressor
I've confirmed that this works with Sonic R (Saturn)'s data files, so if 3D Blast use the same compression that should work too.