Again, you not only must not split infinitives, but you must not separate an auxiliary from its verb; you must say "probably will be," not "will probably be."
"America To-day, Observations and Reflections"
William Archer
The past participle is used to form the Perfect infinitives; as, to have gone, to have seen, to have been seen.
"Practical Grammar and Composition"
Thomas Wood
The infinitives are the parts of the verb preceded by to; as, to go, to see, to be, to have been seen, etc.
"Practical Grammar and Composition"
Thomas Wood