I have a 2N my grandfather bought new in 1945. He replaced the front wheels/tires (I still have them) with 16 inch wheels just like yours. I am sure he got them from the Ford dealer prior to 1950. He had a manure fork he would put on to clean the barn, and I think the 19" tires weren't up to that job.
If they are aftermarket, they were sold through Ford Tractor dealers.
5.50x16 tires would work well on these wheels. Mine is running a 6.00x16 on one side and a 7.50x16 on the other. My dad couldn't find a 6.00x16 when one blew out 30 years ago so the tractor has been lopsided ever since! He had to reverse the rim on that side to clear the spindle, but it works fine otherwise.
I just picked up a pair of matched 6.00x16 automobile tires in perfect condition off Craigslist, so the tractor will soon be on the level!