https://tankandafvnews.com/wo-194-13...ton-chieftain/
This is a study on adding BURLINGTON (aka Chobham) Armor to the Chieftain dated May 1969, and gives you a crude idea of what to expect from 1970s composite armors, and an idea of what Generation I Abrams and Challenger I armor may have been like (give or take about 15 more years of development).
Link to photo showing maximum protection retrofit for Chieftain
Basically, it looks like Panzer IVH rides again.