Target practice??? Back in the days of the N-Series Tractors, additional ballast for wheels was to add Calcium Chloride in the tires. When the Hundred Series models were introduced in 1954, the 600/800, there were what are called 'pie weight sets'. These were 12-segment wedges that mounted on each side of the rear wheels for extra weight. Each 'wedge' resembled a slice of pie hence the nickname. Two weight sizes were offered; the lighter, 29 lb per wedge and the HD set at 45 lb per wedge. The set included a special mounting plate for each wheel plus each 24 special stud extenders also required. The probability as mentioned that your extra holes were a farmerized form of adding some ho-made wheel weight is a good assumption. Ca Chl is a great liquid ballast substance but once it starts leaking into the rims, will destroy any ferrous material. That is why so many original hat rims got ruined. I put Beet Juice ( RIMGUARD ® ™ ) in my 10 (11.2) x 28 8N rear work tires back in the 90's and never looked back -still in there.
FORD TRACTOR PIE WEIGHT SET:
PIE WEIGHT 45# SEGMENT: