I'd roach it too. It will be easier to train & maintain in the long run.
As far as getting him used to clippers it's like anything else horse. Slow and steady. First you let him see them and smell them, rub the body of the clippers up and down his mane with them turned off. Get him used to them rubbing him and the cord dangling down his side (I've never had cordless clippers).
Then you step away from the horse (horse tied up, always practice safe handling) turn them on...and wait for the reaction, if he freaks, I wouldn't shut them off right away. Keep them in your hand and let them run (I'd keep the cover on them or a blade guard in case he wants to sniff them while running) When he calms down and looks at you, I'd shut them off...then turn them back on in a few seconds (8 or 10 you want to keep his attention on the clippers)..see what he does, once he doesn't care about them running, you can touch the body of the clippers to his mane...once he doesn't care about them running on him, you'll be ready to roach.
Please note that this, like any new skill can take one day....or 20 days.
Be patient and post pics!!!
If he just plumb flips out. You can always use scissors, though that will take a few days to get it trimmed just right..and you'll need really sharp scissors that will hold a sharp edge, the ones in the kitchen drawer most likely won't get the job done well.
Be strong and courageous, and do the work. Don't be afraid or discouraged by the size of the task, for the Lord God, my God, is with you. He will not fail you or forsake you.
1 Chronicles 28:20