Problems with my ex racehorse

Question
Hi ya
Recently my sister has moved her pony to a new yard, after settling in a few weeks i have met another horse owner who has an ex point to point racehorse called will and a Egyptian Arab called Joe.  He has offered my to ride Will whenever i want as he is concentrating on his new pony, and if i get on with him i can take him on at no cost.
He is 13 years old so left racing quite a few years ago, he done very well and won many of his races.  Since then i don't think he has been re-schooled as all he has been used for is walking on roads and though fields then a gallop when he wants, he has also done alot of hunting which is also fast paced work.
The owner has told me a few don't such as don't turn him on the spot as he will gallop off, and if i walk up any path to a field when he reaches the field he will gallop off, as you can imagine this will be quite annoying and i want to break these habits.
I road him for the first time today in a little paddock at the farm so as he had no where to bolt off to, he had a lovely walk and listened to my rein aids.  But when it came to trotting i slightly shortened my reined then with a slight nudge he jumped into canter, i brought him back to a walk but every time i retryed to make him trot he'd jump back into canter.  I think from what he has been used for since racing he hasn't been trotted much, Do you no any way i can teach him to trot without jumping into a canter?
I have been told he is 100% on the roads and an going to try him out on some quite roads to see how he behaves.
One other problem i have got is hes very nasty he has never bitten any one but once you start to tack him up he throws his head every where and threatens to bite all the way up until i get on him once tacked up he is a night mare he will let me touch his face but no where else, without snapping and kicking his hind legs out.
I am an experienced rider but as you can see i have come across a few problems that i am stumped at
Please could you help
Much apprieciated
Zee

Answer
Hi Zee,
         This is a very complex problem however I believe you have touched on the answer in your second paragraph.
Re-schooling is what is needed.
Years of encouragement to do what he was bred to do can not be undone without a lot of time being put into retraining and building new habits.
Reading between the lines, you are a caring person and very capable of winning this test. You have identified what the problem is and all I can do is endorse the actions you have already started.
Set little bench marks and work on one thing at a time. When he has got the message, move on to the next.
I am sure this will be a rewarding experience for both of you and you will be a much wiser person by the time you have completed your task.
Your reward will be in a horse that respects you and enjoys doing what you want him to do.
Good luck,
Don Boddie