Dogs tolerate simple (acetylsalicylic acid) aspirin products (offered only on occasion; they may cause stomach upset or ulcers if given too frequently, plus they are a blood thinner, so it may completely inappropriate in some animals). For the most part aspirin products should not be given more than once in a 24 hour period and never longer than 3 days without a blood chemistry done to be sure there's no internal damage being done.
A 64 lb dog should be able to have one (320-325 mg) adult aspirin. Your big dog should tolerate two aspirin.
The average dosage for regular aspirin is best kept at about 5 mg per lb.
It's vitally important to the dog that owners discuss options with their veterinary caregiver. It's far easier to avoid a mistake than to treat a poisoning problem.
Also, if this paw swelling is the result of a bite (allergic reaction to a bug bite) you may want to try a Benadryl.
As with even the aspirin, Benadryl ( Diphenhydramine, for allergies) should never be given without a veterinary recommendation. Dosage is typically .50 to 2 mg per pound of body weight just one or two times a day. Starting with a 1 mg dose is usually recommended.
Tablets usually come in 25 or 50 mg doses.
Liquid Benadryl is not recommended.
I hope he feels better soon.