As mentioned, the T-bars assembly has two parts, the lifter (lower piece) and the striker (upper). As far as I can tell the lifter is the same on the two examples I have.
The striker body proper, separate from the one, right side pin lug, is the thing to measure. It is a little futzy to get a dial caliper on, but can be done (unfortunately you have to remove the T-bar from the rifle.
The striker of my 'problematic' T-bar (and perhaps the FTF rifles tend to share this) is .372" tall.
The 'new' striker is .406" tall. It also, visually, has a very obvious angle from the slight 'rolled' top tip, back (about 45 deg.) whereas the original was mostly square topped with just a slight chamfer back at the rear edge.
The thickness of each is: old, .153"; new .1505" (this is essentially the same for practical purposes and manufacturing tolerances; it affects the final firing pin protrusion as it interrelates to the hammer stop.
As I understand it, all new production (no idea where the actual transition is) is using the 'new' style, which may be a return to an earlier T-bar, but I dont have enough models/years to know.