Out of curiosity, have you considered using Porteus
as your base? I am using the XFCE variant with root login, and it didn't take long for me to customize it with the tools I need (the distro makes it *really* easy to do so). It's designed to be run as a live distribution and they stuff in a ton of tools to make customizing it easy. It's based on slackware, same as parted magic was.
All you need to do is get the variant you want (xfce seems to run more stably then lxQT), download and repackage the programs you want to add via the USM program, then make the changes you want and use the porteus manager while running to save the session itself as a package.
Here is some screenshots of me setting up a custom build (less then 300MB) similar to parted magic after about 2 hours of fiddling.
Here is my desktop after loading porteus into RAM. I also put in a boot option that prevents drives automounting (which will hang the boot if a drive is especially faulty).
Firefox opened up, with everyone's favorite new adblocker, µblock
GSmartControl, ddrescue, and thunar file manager all open
Windows network share all fine and easy to access, which parted magic always struggled with (requires the gvfs package)
A quick look at the main customization menu
Porteus 32 & 64 bit (and both EFI and legacy) on my USB drive. You'll notice both variants are below 300MB each, that includes printing support.
All the packages I made up and included to get it more parted-magicesque. Here is the list:
[*]first three are just internal updates brought down by the porteus update manager
[*]changes-150428.xzm is all the changes I have made to the session (firefox customization, shortcut changes, that sort of thing). This was made via the porteus save session option (done on a clean boot after downloading all the packages first)
[*]ddrescue - Pretty self explanatory, very useful drive rescue tool
[*]grsync - graphical interface for rsync, which I find is a *really* fast copy tool
[*]gsmartcontrol - hard-drive testing tool, same one parted magic used
[*]gvfs - So the file manager can hook into windows shares easily
[*]hfsprogs/utils - HFS access for apple filing systems
[*]testdisk - partition recovery
That's just the ones I bothered with, I'll probably add more packages as I need them. But yeah. No need to reinvent the wheel (though it looks good so far).