Hi,
I've just reached my 4-year anniversary of the same operation as your father. At the time, I was 66 and told that I would be treated "aggressively" !! My normal weight at the time was 75-76kg which dropped to 68kg due to the cancer. During treatment (chemo, more chemo and combined chemo/radiotherapy) I managed to get to 77kg and now I'm consistently 77-78kg.
My wife, Patricia, contacted the Cancer Council (NSW) regarding a suitable diet pre operation. The hospital provided a dietitian to advise specially for oesophagheal cancer patients - it so happens she said my wife's regime was spot on and we've stuck to it since.
As explained by my surgeon, the repositioned stomach is of course smaller in capacity and not flexible in the higher position - hence, obviously, I can eat only small meals (about 400ml) more often and drink in between.
Feel free to ask any questions, talk, etc.
Kindest regards,
Bill