To make huge sprites like that is pitifully easy. All you do is have several 32x64 sprite blocks arranged in a set pattern, like so:
1 2
3 4
etc. And for each sprite, assign its memory pattern to adjacent areas in video RAM. Then, simply block copy the sprite data to the first pattern location (normally somewhere between 0x4000 and 0x5000 for us indies, but official developers of the time didn't always follow the same rules) and you're done.