When parts get shuffled among different cars, as tends to happen after 40-50 years, it can be very puzzling when parts don't fit like you think they should.  For instance, take a look at the front disc brake stone shields in the photo to the left.  We have identified 5 different styles so far, and when used in the wrong combinations with two different brake caliper mounts, two different size rotors, and three different caliper types, parts may not fit together if the proper combinations are not maintained. Take a look at each of the individual photos below as I explain what parts are to be used with each different style of stone shield.  I have also included the correct type of caliper mount in the photo for each style shield.  Don't forget that there are specific parts for left and right sides on all of this except the brake rotors!
This is the TR3A style stone shield.  The early disc brake cars (smallmouth) and very early TR3A's did not have any stone shields when new, and they were added sometime after the introduction of the TR3A.  Brake discs are 11" and the calipers can be either type A or B.	This is the very early TR4 stone shield, for cars up to approximately 6350, depending on whether the car had disc or wire wheels.  These were the cars with the TR2/3 style front suspension with 0 degrees of castor, and used 11" brake discs with type B calipers.  Note the large square hold to give clearance for the outer tie rods.
By the time the TR3B's started production, the TR4 was well past the change point above and the switch was made to type C calipers and 10.75" brake rotors.  Note the new style caliper mount, and the change to a circular opening at the center.  Also take note of the mounting tab angle, which has changed significantly from the earlier stone shields.	Here we have the later TR4 stone shield, similar to the TR3B type for use with the 10.75" brake discs and the type C calipers.  You see that this shield has the outer tie rod clearance hole just like the early TR4, but mounting tabs and inner cut-out have changed for the new style caliper mounting bracket.
With all of the front suspension changes at the introduction of the TR4A, a new stone shield design was needed.  The "late" caliper mount is unchanged for use with the 10.75" rotors and type C calipers, but the large square for outer tie rod clearance is gone, and the small relief slot for the lower trunnion has been enlarged. This stone shield design was used through the entire TR6 production, meaning everything with the IRS style frame TR4A-TR6.	Here is a better look at the center cutout design and the mounting tab orientation, between the early design for 11" rotors and type A & B calipers on the left, and the later design for type C calipers and 10.75" rotors on the right.  There are enough differences here that you'll have an impossible task fitting everything together and making it work without a sailor's complete vocabulary!