Ishraqi

The Bhavishiya purana has no mention of Nanak.But then again for a text that was composed after Islam came to India I wouldn't be surprised that some "prophecies" were added...

There is no mention of any Nanak in the Bhavishya Purana. It's one of these very late puranas in which everyone wishes to see whoever they want to see in it. What is probable is that Gurbachan Singh Bhindranwale interpreted Kalki avatar to be Guru Nanak as does Tara Singh Narotam in his chapter on avtarvad in his Gurmat Nirnay Sagar.

On the subject of Bhai Maharaj Singh you can read:

Ahluwalia, M.L.1972.Sant Nihal Singh alias Bhai Maharaj Singh, Patiala: Punjabi University.

and

Mehar Singh, Giani.n.d. Nau Ratan, Ludhiana: Lahore Book Shop. pages:123 to 163.

They shouldn't be too difficult to find.

The reference to Guru Angad being Janak in a past incarnation is found in the Bhattan de Svayye:

You hold tight to the Naam, the Name of the Infinite Lord; Your expanse is immaculate. You are the Support of the Siddhas and seekers, and the good and humble beings. You are the incarnation of King Janak; the contemplation of Your Shabad is sublime throughout the universe. You abide in the world like the lotus on the water. Like the Elyisan Tree, You cure all illnesses and take away the sufferings of the world. The three-phased soul is lovingly attuned to You alone. O Kal, chant the Praises of Lehnaa throughout the seven continents; He met with the Lord, and became Guru of the World. || 3 ||

(section in praise of the second Mehl)

The same reference is made about Guru Arjan in the section in praise of the fifth Mehl:

|| The benign rule of Raja Janak has been established, and the Golden Age of Sat Yuga has begun. Through the Word of the Guru’s Shabad, the mind is pleased and appeased; the unsatisfied mind is satisfied. Guru Nanak laid the foundation of Truth; He is blended with the True Guru. In the House of Guru Raam Daas, Guru Arjun has appeared as the Embodiment of the Infinite Lord.

The term "historical reference" used by N3O is inappropriate, first of all because Janaka is not mentionned in historiographical accounts but in the epic poem Ramayana by Valmiki, secondly because the reference in this case is a textual one not a historical one.

Mirpuris are a total disgrace.