Emulator for Everdrive
If you put gb.v64 and gbc.v64 from the download link above into the folder ED64/emu on your everdrive you can play gameboy ROMs directly without having convert them individually.
Use a bios to get the gameboy startup animation with the nintendo or gameboy logo. Don't include them to skip the animation and boot directly into the game.
Use SRAM instead if you have trouble saving on 64drive.
Pad to MB
Retroblaster requires the ROM to be an even multiple of a megabyte. Check this to apply padding to the output ROM to size it up to the next MB.