Someone on here posted a link to a walbro parts diagram. It had all the info. I will post the link once im done work. Unless someone else beats me to it.
One way to tell what size carb, is to look in the throat, and there should be a number stamped in there. It will be the venturi size in 64ths of an inch. Take that number and convert to mm's.
Im actually really surprised that the repair guy didnt know what the needle was on that carb. All the single needle carbs ive seen, had a preset low needle, and the adjustable one was the high speed needle. It should be stamped with an "H" near it.