I personally prefer to use a very sharp knife and a pair of clamp emasculators, held for 10 sec. Very little if any blood and heals quick. Cut high up into the sack and push covering tissue up over cord high 1/2 - 1 inch over testie, then clamp and hold, all done.
I would give him his first round with a tetanus toxoid, wait 3 weeks do it again and castrate. Get him on feed good, worm and treat for flies, with a pour on such as Cylence, works great lasts for a few weeks, then retreat when you see flies on his back.
Good luck, OH, give ALL shots in the neck Only! or Sub Q as per lable instructions!