Here are some part numbers for servos taken from my Unipart brakes catalogue:
1500/TC 1970-76 64049508
2000/2500 1969-77 SSB72670
Dolomite 1300/1500 1976-78 64049502 1978-81 74049207
Dolomite 1850 1972-78 64049508 1978-81 64049689
Dolomite Sprint 1972-75 64049689 1976-78 64049508 1978-81 74049207
Stag 1970-77 SSB72667
Toledo 1970-76 64049502
I understand that the SSB numbers are Lockheed and the others are Girling.
No more detail given I'm afraid.
James