Thomas Merton's "spontaneous prose" is to be found in the seven volumes of his journals. That's where you will find the real Merton in all his depth and complexity, his faith, his doubts, his inner (and outer) conflicts, and his endless self-examination. I never tire of re-reading them.
This essay by Angus Stuart delineates some Kerouac-Merton parallels.
"Even the timing of their own deaths is remarkably close: Merton on December 10, 1968 and Kerouac less than a year later on October 21, 1969." Kerouac died of drink at age 47, Merton of electrocution at age 53.