modifier 50-billing on UB Hcpc 73630

1 unit. If you look in the Medicare guidelines as well as most commercial carriers instructions, 50 modifier is reported with 1 unit.
Consider looking at your claim submission thru the eyes of a payer too, and sometimes that will help. In your case if you submitted it with modifier 50 and charged for two units it would be like telling the payer that you were requesting for reimbursement for Left and Right side done two times? Just a thought...