Get a top quality, well fitting muzzle.
Keep it on him at all times if there is an occasion where a bite may be possible.
Get many helpers as you can possibly find, of as many and as differing appearance as you can possibly muster.
Have your helpers come around and start from completely ignoring him to gradually working up to as much interaction as possible without causing a reaction.
Very slightly increase the interaction with each positive reaction you get from him, pull back slightly with each negative reaction. Reward positive reaction, and ignore poor reaction.
As with any training, keep a log of all that you do and the results including a tally of positive and negative reactions and clear definition of steps.
You should have a clear picture of where you are and where you need to go in a fairly short time.
ONLY remove the muzzle when you are completely sure of his reactions.
This should take care of your problems.
"I'd better go with you Huck, civilization can be dangerous."-------Tom Sawyer(Mark Twain)