The hole by the flywheel is difficult to find - and in fact I dropped the starter motor off when looking for it. In fact a junior hacksaw frame is almost perfect for finding it - and it can be accessed with the motor in place. Its on the casting above and in from the top flywheel bolt.
I had a Draper kit with a bent bar which was 8.06mm diameter and wouldn't fit (even after I'd found the hole) I don't think an 8mm drill would fit either but a 7.5 would. The hacksaw is slightly smaller but as the only adjustment is whole teeth it won't make any difference either. (Slack in no way equates to one tooth)
Is the 16mm deep socket for the bottom pulley bolt? If so - you don't need to remove it. Just remove the bit of plastic round the crank pulley (2 small bolts) and the belt will come out without excessive twisting.