I asked SRM about them during the holidays and they finally responded with the following.
ours are correct length of 6.469" centres, the material is stronger then a forged material, it is an alloy, 7075T6 condition ,material extruded under a huge BAR pressure , so gives similar properties to a forging plus the material is a modern and very strong material .
Width of bean is slightly more than original BSA, so the cutouts in cylinders may have to be widened a bit to take the rods.