Yeah - I just did my m543a2 - basically the same bed with a multifuel and old m52 series cab - anyhow I used ~100ft of wire rope (IWRC extra improved plow steel with a steel core); I run 3 parts of line (off the tip of the boom, through the block shiv, back through the second boom shiv and then the fixed end back on the block.) I would stay away from fiber core unless you only plan on doing light duty stuff...
When I went to overhead crane inspection cert training the idea of fiber core rope in use still was laughed at...
You can put the electroline fitting on the end of bare rope that you get from any rigging or crane shop - although you might do well to buy a new electroline fitting as they are often near impossible to field strip if they have been assembled properly and loaded with any sort of significant weight...
When you strip back the rope and untwist the lays I find it works well to use a hose clamp to keep the lays from spreading too far (just remember to put the securing nut on the rope first
)
Good luck
Matt