LDArc and LDIFF
From Just Solve the File Format Problem
LDIFF (or LDiff) is a differential compression utility for DOS, designed for binary files. It was developed by Kazuhiko Miki (also known for LArc). Its native file format is .LZD.
Identification
LZD files created by LDIFF v1.20 have "-LD6-"
at offset 2.
The format has some similarity to LHA, but is not compatible with it.