If you need front brake calipers, go to a Datsun (excuse me - Nissan) dealer and get 4 new calipers for a Datsun 2000 ('60's vintage). They used the same 2 1/8" calipers that all the ser.1 E used. They still make them and the price is low. You can even put them on the rear as a group of all 4 instead of the original 1 7/8" Jag had. Have put all 8 on Jags for years with no ill effects on cars used for hard driving, autocrossing, and vintage racing. Since the fronts do most of the braking, the small difference is not noticed.
A mechanical engineer once worked out all the numbers and the difference in the rear was only a few percent.
Also, the caliper change in '68-'69 used very different rear and front calipers, but used the same master and booster. Yours is the early 3.8 system which used the same F & R calipers up to the ser.2.
Phil.