U Ba Khin and his reference to Parajikan Atthakatha

Monk Sarana has been so kind to let me know the existence of an English translation he is aware of (now out of print but digitalized by him):

Shan-Chien-P'i-P'o-Sha
A Chinese version by Sanghabhadra of Samantapasadika,
Commentary on Pali Vinaya translated into English for the first time
By Prof. P. V. Bapat, Poona
in collaboration with Prof. A. Hirakawa, Tokyo
Bhandarkar Oriental Research Institute, Poona, 1970

This is a complete translation of the Chinese version of the Vinaya Commentary, so not exactly corresponding to the Burmese version that U Ba Khin could have used.

The Anapana section starts from page 358 to 381 of the PDF file. I was not able to find a passage similar to what U Ba Khin was mentioning. A possibile candidate may be the following, where after emergence from strong samadhi (fourth jhana) one contemplates its physical base:

[20] [How does he stabilise it? This Bhikkhu emerges from the Fourth
trance. He- firmly grasps the factors of the trance. When he has grasped
this, [he sees that] these factors of trance are depending upon the heartbasis
which, in turn, is based upon the Four Great Elements; the contemplation
upon Four Great Elements is [also] based upon his physical
body. Out of these, the factors of a trance are called non-material and(heart-)
basis and the rest material. The non-material dhammas are to cover consciousness.
Out of these [dhammas ], the Four Great Elements and the like
are material and mind accompanying those material qualities, is nonmaterial.
Or, when he emerges from the samadhi, he notices that the body
and mind are the source ( ... ) of the out-going and in-coming breath.

Incidentally but interestingly, what should be the same passage as translated from the Visuddhimagga and reported in the other answer is here rendered differently:

Thus -he has discriminated Name from Form and then he seeks their causal factors. In all the three worlds, the Name and Form are inseparably joined; they are never severed [from each other]. Regarding this inseparable connection, he begins to have some doubt. But he overcomes that and then notices three characteristic marks. Having noticed these three characteristic marks, he further reflects upon the coming into and passing out of existence. Because of this contemplation upon the coming into and passing out of existence, he first notices the [illusion of] light and gets rid of the ten minor taints of the penetrating insight (vipassana'). [22] When he has got rid of them, there appears the Knowledge of the Path (...). When this has appeared, he abandons thinking of the coming into existence and has his attention directed only to the passing out of existence. Then he again and again reflects upon that characteristic of the passing out of existence and when these two dhammas (coming into and passing out of existence) have now become clear to him, he begins to have a sense of aversion [for all things] in this threefold world. And then in due succession, he attains the Four Paths and reaches the Fruit of Arhatship. He attains the highest stage of the nineteen types of deep knowledge (...) and in this threefold existence consisting of Brahmas, Maras, and Samana-Brahmanas, he reaches the highest stage of being the field of merit (...). Thus is concluded the first tetrad of the detailed explanation of the mindfulness of Anapana [commencing with ] counting.

Also as we can see (in bold) the word "kalāpasammasanavasena" (if even present in the Chinese version) is interpreted differently. Bhikkhu Ñánamoli rendered that as "comprehension by groups", and it seems not related to the kalapas as groups of the four elements, that is to what U Ba Khin was intending.