Like Lemonhead [what an unflattering name] i also checked out the Yella Terra site.

The only rockers that were listed on the site for the "A" series Datsun were the 1.55 to 1 ratio rockers which were on offer as a kit,[YT16023] containing the rockers, the shaft & the pedestals, which leads me to suspect that the ratio is increased by moving the shaft closer to the pushrods to allow rocker length variations.

Like others, i look foward to Lemonheads next post.