Welcome Jeff
Your father would have been in the 1st Battalion of the Royal Sussex, which was part of the 7 Indian Infantry Brigade, which in turn was part of the 4th Indian Infantry Division.
They saw some very heavy fighting at Cassino. A good introduction to the 4th's Italian campaign is:
The Tiger Triumphs. The Story of Three Great Divisions in Italy. 1946. Foreword. Table of Contents.
A good book is (though it only gives minimal mentions of individual Regiments):
Amazon.co.uk: Cassino: The Hollow Victory - The Battle for Rome, January-June, 1944: John Ellis: Books
Have you applied for his Service Records? They will contain very similar details to the service books you have but may contain additional info.
If there's anything specific you'd like to know then ask away.
Ron was a wireless operator, and I'm sure he could help on providing information on that front.
And you maybe interested in this:
BBC - WW2 People's War - The Hell of Monte Cassino