Seiko actually launched two limited edition watches to commemorate its milestones in mechanical chronograph movements. Apart from the SRQ031J1, Seiko also launched the SRQ029J1. While the SRQ031J1 honoured the 1964 milestone, the SRQ029J1 honoured the 1969 milestone instead. The 1964 milestone is Seiko's first manual winding chronograph while the 1969 milestone is Seiko's first automatic chronograph, the 6189.
I already have the SRQ029J1 in the collection (please click here to go the full review) and the acquisition of the SRQ031J1 completes the collection.