Welcome to the forum. No better way to learn than what you are going to do. Take down, clean, repair, and rebuild. You will have fun. As far as the stock bolt go, the guys above are correct for normal take down. Additionally, the end of the threads are typically upset or peened to prevent unintentional loosening. During one rebuild project I did use one old USGI stock that was in pretty good shape except it was obvious that the stock cross bolts were badly corroded. You can remove them by center punching the flat side (opposite the bolt handle) and then drilling thru the head with a bit just slightly bigger than the bolt shank. When the head is free, you can drive the body out from left to right. The bolts are harder than the gates of He!! so I suggest a carbide bit if possible. New cross bolts are readily available. Enjoy!
EDIT: By the way, if you do in fact need the spanner wrench, just get a cheap screwdriver that you can live without and take your dremmel with a cut-off wheel and nibble out a notch in the middle. Keep it simple.