removing ignition

wanting to remove cover from cases and points, the small bolt that is 17 mm i think, is there a trick to getting it out. I have heard horror stories of breaking these bolts off in the crank, and for sure dont want to do that, which one should i try to turn, the larger nut or the smaller bolt that screws into the ign assembly.

If you are triing to remove the advancer. Turn the 13mm /small bolt, the 17mm will turn the motor over the 13 will loosen and the advancer will come loose
I did it wrong and sheered the pin on the crank 2 weeks ago so its fresh in my mind LOL

do I need to mark the location of the ign or advancer, dont want to put it back wrong and screw up timing.

Theres a notch in the back of the advancer that fits to the pin on the crank. Maybe to be safe if you tearing down the engine, set the timing mark and 1 cylinder at top dead center and note or take pics as how it was when taken off
{and I think the pin can come out of the crank easily so dont lose it. Its only about 3mmx5mm or so}