If you use studs, no AntiSieze in the portion threaded into the block. You want them to stay, and to stay forever (figuratively). AntiSieze on the nutted section is a good idea.
You only need a stud slightly longer than the bolt you're currently using to allow the stud tip to extend beyond the nut. I used ARP studs for my 550/500 bikes, and ordered them in 32mm.
I think I know the size, I'm guessing m8x1.25. I'm pretty sure that's right from when I helicoiled them. I'm gonna say length of stud is 25-30mm. You could always run a but on and trim them if they are oversized
For a stud- no anti-seize and run a normal torque, don't crank like a maniac to 'make sure they don't unscrew'.