I am pretty sure about 30 peanuts make up a tablespoon (one serving) It's on the container of unsalted peanuts.
I don't see why you wouldn't be able to substitute it for ANPB. Go for it!
just take the serving size in grams and divide by the grams of fat per serving. Then take that number and multiply by the grams of fat you're supposed to eat for your meal. That will tell you the raw weight in grams. Then just get a gram scale and measure it out.
40 nuts or so is a serving with the nuts without shells. Unsalted would be better, less sodium content. Either way, yes, you can. Look at the ingredients on ANPB. Peanuts. Sometimes salt.