The Khaḍipadā image inscription is largely overlooked in historical studies of Vajrayāna, yet it seems to be tremendously important. The publisher of the inscription, A. Ghosh, assigns it to the seventh century on palaeographical grounds (Epigraphia Indica XXVI 1941-42, pp. 247-248). The short inscription was found on the left edge of a Padmapāṇi statue. It records the name of the king under the rule of which the donation occured, the name of donor, and the name of the craftsman who incised the inscription:
oṃ śrī-śubhā(or śuhā-?)karadeva-rājye mahāmaṇḍalācārya-paramaguru-rāhularucināṃ tasya dedharmmo yaṃ | utkīrṇṇaṃ kuḍhā(?)-sūttradhāreṇaḥ ||
The rendering is a bit uncertain. As Ghosh suggests, de dharmmo obviously stands for deyadharmmo, and we should probably ignore the visarga in sūttradhāreṇaḥ. Ghosh proposes rāhularucināmā for rāhularucināṃ which is also feasible, but I'm not really convinced. So the text must means something along the lines of:
Oṃ. During the reign of śrī Śubhākaradeva [of the Bhaumakara dynasty, there was a man] called Rāhularuci, a chief maṇḍalācārya and royal preceptor. This is his pious gift. Incised by Kuḍhā, the craftsman.
Niceties aside, the most important facts are that there was a guy called Rāhularuci, a very Buddhist name, who was a 'paramaguru', a title reserved for the royal chaplain, and he was also a (mahā)maṇḍalācārya. This, as far as I know, is the earliest occurence of the term maṇḍalācārya. The fact that the royal preceptor is a Buddhist also seems quite unique. The Bhaumakaras should be given much more attention.
PS: due to an unfortunate data transfer I lost the link to Mori's website which had a photo of this particular Padmapāṇi statue. I'd be very grateful if someone could post it.