Q: Software for porting Mac HD to PC via USB sled?

Mac uses hard drive formatting that is foreign to Windows, so windows cannot read or mount a drive formatted for Mac.

You will need a Driver that can enable Windows to read that file system.

Assuming its formatted as HSF+  You can use this:

https://www.paragon-software.com/home/hfs-windows-free/

Otherwise, you'll need to find out what your hard drive is formatted as and search out a windows driver for the specific type of formatting.

As I told you above, If its formatted HSF+ you can use the Paragon driver I linked to above.

Otherwise it will depend on how its formatted.  You need to find out what format its using, and then find the driver for it.

You will need Java installed on your new PC and this software Catacombae - HFSExplorer. It allows you to explore and copy, data off your old Mac's HDD.