It appears you do not have to do any partitioning ....... just use the "oldboot" partition to fully install PCLOS into.
There is no need to wipe it .... that would be done during the install, after you have selected that partition as the target for your install.
In your situation I would take this route ..... yes it has the effect of overwriting the Win boot manager link in the MBR with Grub, but if you need to revert later it can be easily done from a Win CD.
The Grub boot manager will give you an entry to boot into Windows as well as the options for PCLOS.
If going this route there is one thing to keep in mind .....
under 'normal' circumstances the automatic install would create three partition ..... one for the OS itself designated " / " , another for user files designated " /home " and a third a Swap partition for cases where you may run low on memory.
When installing to a single partition you only use " / " and the user files are automatically placed in the same partition. It is not "ideal" in lots of cases, but should be sufficient until you become more familiar with such schemes and want to change things.
If you should discover you need Swap due to running low on memory, then a Swap file could be created, rather than a partition allocated to Swap.
That is just my view of things ....... others no doubt will have different ideas ....... that is the difficulty with Linux --- you are expected to make choices
Hopefully there will be other suggestions for you to consider
Oh! Almost forgot ........ Welcome to the forum