All,
I am using post 81 brembo calipers with a 1979 master cyclinder specified to be used for the ATE calipers you are having trouble with.
The master cylinder is of a different bore that that supplied eith the Brembo's, so the braking experience is different. If anything the brakes work too well, with little progression. However they are strong and work okay. Eventually I will swap the master cyclinder to match the calipers, when I find a serviceable one cheap.
I did this because, at the time, it was cheaper to buy second hand brembos that it was to buy an overhaul kit/s for the ATE's.
No modifications were necessary. I also changed the lines at the time for stainless steel BFGoodrich items, but I suspect this was the step too far - i.e. with regard to progressive operation.
Steve H