It should? The spoiler one is for the drivers side so for RHD’s on the right side, no?
They are a slightly different shape, in that the spolier arm is slightly more "bent " than the other. The spoiler on the LHS allows both arms to sit lower and more parallel to the base of the screen. As can be seen on your car the spoiler on the RHS means the outboard end hits the base trim . The later wiper arms are different and are the same shape but early ones like yours are handed.
In any case the spoiler makes bu**er all difference in my experience and as has been mentioned the wiper system in general is not very good with limited clearing for RHD cars, and hardly brilliant for LHD versions. A compromise, which I use, is a slightly larger blade on the drivers side. Remember the 50 year old system is not that powerful and very large blades will put considerable extra strain on the motor and linkages.
Simple answer dont drive in the rain!