Brendan:
You should have said:
These are some notes that I compiled some time ago for internal use in a magazine with which I was involved.
or
These are some notes, which I compiled some time ago, for internal use in a magazine with which I was involved.
And not:
These are some notes which I compiled some time ago for internal use in a magazine that I was involved in.
You should have said:
These are some notes that I compiled some time ago for internal use in a magazine with which I was involved.
or
These are some notes, which I compiled some time ago, for internal use in a magazine with which I was involved.
And not:
These are some notes which I compiled some time ago for internal use in a magazine that I was involved in.