3.
W.e.f 01.02.2019, relevant portion of Section 17 (5) (a) reads as follows:
"Notwithstanding anything contained in sub-section (1) of section 16 and subsection (1) of section 18, input tax credit shall not be available in respect of the following, namely:-
2[(a) motor vehicles for transportation of persons having approved seating capacity of not more than thirteen persons (including the driver), except when they are used for making the following taxable supplies, namely:-
.........................................."
As buses purchased by you are 56 seater, ITC there-against is NOT blocked under above provision. In other words, you are entitled to avail subject ITC.
Case-law pointed by Shri Kasturi Sethis Ji points to same direction even if same are related to 'renting / hiring services of motor vehicle having approved seating capacity of more than thirteen persons (including the driver)'.
These are ex facie views of mine and the same should not be construed as professional advice / suggestion.