You shouldn't try to convert lha's to adf's.
.ADF is a disk image and is usually a self-contained, bootable image of a floppy disk
.LHA is a file archive. The operating system needs to be up and running in order to access the contents of the archive (the files) using the LHA program.
So look out for an image of the operating systems.
Cloanto's Amiga Forever and
Amiga In A Box come to my mind. You can also start by using ADF's of the original Workbench install disks but this is going to take much longer.