His conversion is disputed because he did not confide in his wife or daughter Holly, who later edited his poems and letters.
I just googled it and found the letter from Father Hanley, who baptized Stevens in the hospital. I see no reason to doubt what he says. Naturally most modernist literary critics prefer to put the whole business down the memory hole.
http://www.writing.upenn.edu/~afilreis/Stevens/conversion.html
Sunday Morning is a wonderful poem, and lines from it have occasionally popped into my mind at odd moments over the years...
The letter from Fr. Hanley is very interesting. 1977. This was not a great time for the Church, but there were still good priests and devout laypeople and it sounds as if he was fortunate enough to find them.
I know this is probably a silly consideration, but I have always worried about artistic converts - that is, people attracted by that aspect of the Church’s vision of the world - after the total collapse of church art, music and language following VatII. I know Graham Greene basically left because of that, and I have always been glad that some illustrious artistic converts - such as Edith Sitwell - didn’t live to see the “stripping of the altars.”