Extra length of 0.220" for 8 port Arden heads on 1275cc. Larger 6.35mm diameter 3 piece push rod (2 ends and 1 rod) which needs loctiting for safety although once fitted the parts cannot displace.
The larger diameter improves push rod rigidity as much as is feasible
without having to modify the block/head push rod ports. This in turn better translates the cam lobe profile at the valve which therefore improves engine performance. Particularly where up-rated/stronger valve springs are used.