The reason why the split block was specified and insisted on by H&H initially was because the spec stated that the rifle must be as per the drawing with the addition of the pads. IE, with a split block and 5 grooves. So any that came through NOT to spec were initially rejected. But later H&H were (presumably) informed that these variations W"ERE the amended acceptable spec so were therefore acceptable.
The conversion specification stated that the letter T was to be added close to the rifle designation to indicated its change to telescope status and subsequent change in its Ordnance designation/classification.