Hello and welcome. My name is ***** ***** I have been in the dog field for 25 years. I am a Therapy Dog & AKC Evaluator/trainer/ as well as an assistance/service dog trainer, specializing in behavior. It will be my pleasure to help you today.
Given the age of the dog any traquilizer may be dangerous for you to give at home. A Vet is going to want to examine your dog before giving anything as well.
There is an over the counter medication called melatonin which helps with dog's anxiety. I would give this for about a week before attempting any grooming. Unfortunately this pup has been aggressive all of its life from the sound of it so it will take time to get one paw done in a pleasant way so that dog accepts it.
This is going to be time consuming due to the personality but I would use a reward for all good behavior , something like chicken sliver or hot dog sliver after you briefly touch the dog. The more you can reward the good behavior with something special the more the dog is going to accept you touching it.
Generally dogs that lash out like this are naturally afraid of people, so when we continue to go near them with all the snarling and barking, they feel threatened, this makes them lash out and bite.
Also the way the dog was handled when it acted out had a lot to do with how that behavior increases or decreases.
If grooming must be done immediately, then it may be wise to invest in a basket muzzle so the dog cannot bite and it may be worth investing in a grooming hammock so you can safely do the legs , feet , and face. You can probably reach the back of the dog safely as well.
Benadryl is another medication that sometimes makes dogs drowsy so you may want to try that first before the melatonin, just to see if the dog will become drowsy enough for you to groom a foot.
Melatonin found in drug stores by vitamins
This is a basket muzzle which still allows the dog to pant and take a treat from you, but will prevent it from biting you