Like src-32, src-16 builds two versions of the boot program for a given card, card.rom, and card.lzrom. If you want to test from a floppy, prepend floppyload.bin before writing raw to a blank floppy or use the .fd0 targets in the Makefile. All this is just like the src-32 version.
Currently only booting tagged images (see documentation) is supported as I don't know when or if Linux/ELKS will support booting off a NFS mounted root. To make a tagged image see the directory netboot-*.