Randy is right. Those are original. They are spacer shims and are installed on the RH (passenger) side to level the car, to make allowance for the driver's weight on the opposite side.
I guess this sort of assumes that the car will be driven without a passenger more often than not. Hmmmm. Maybe Triumph thought their typical buyer was a loner, a single guy who wasn't likely to have a girlfriend or wife. /ubbthreads/images/graemlins/wink.gif
Levelling like this will actually help balance the car's handling a bit, too. So actually, I think it's done since nearly all racing is done without a co-pilot... an exception being rallying.... and by the late 1950s and early 1960s Triumphs had become quite popular on the track.
Really serious racers buy expensive platform scales and carefully weigh all four corners of their cars on a level surface to adjust ride height and balance weight distribution, which in turn "tunes" cornering, acceleration and braking. It can be changed and tweaked from track to track to adapt to local conditions, speeds and car setup. This adjustment is usually done with shims or wedge blocks under leaf springs, spacers or otherwise adjustable perches under coil springs.
Watch the guys in the pits at a NASCAR race sometime and you'll see a lot of this going on. They are adusting a number of things as the race goes on, trying to balance the car's handling as best they can. It effects front and rear grip and can really change the speed of the cars coming out of a corner, as well as how early or late they need to brake, and how hard, going into a corner. The setup constantly changes, as tires wear and the track heats up, the car consumes fuel and gets lighter, etc. This sort of ultra criticial fine tuning is not very practical for a street car, of course!
Sometime earlier in TR2/3 production spacers weren't used and viewing one of those cars from behind - when only a driver is onboard - you'll be able to see a definite "lean" to the left (on a LHD car). The spacers were eventually added to correct for this.
A lot of folks working on cars that have them accidentally put the spacer leaf back on the LH (driver) side during reassembly, not stopping to think that with the axle positioned above the springs, the spacers act to lower the car, and thus is needed on the side that is lighter (lacking a passenger's weight).
Of course, on a RH drive car, the spacers would be used on the opposite side.
The heavy duty/competition rear springs for TR4 did not use a spacer on either side. AFAIK the later leaf springs with a lot more arch and very large aluminum spacers didn't use them either.