I'm guessing that the weight of a 1/2" long tack is about a penny weight = 2.3 grams.
I'm also just guessing that the weight of an N flywheel is about 50 lbs.
50 lbs X 16 ounces to the pound X 28.3 grams to the ounce = 22,640 grams.
One tack is about 2.3 ÷
22,640 = .01%
I seriously doubt that when the flywheels were new they were within .01% in balance.
Secondly, I suggested four tacks around the circumference of the flywheel. Lets try to make them reasonably equidistant and let's say any decent welder can make each tack within 10% the same size and weight.
So now we are looking at 10% of .01% out of balance. If my arithmetic is right that is about .001% out of balance.
Do you really think that matters??
Do you think even Formula 1 race cars are so exact?
Ever heard of a slitting wheel for a 4" angle grinder? They are about 1/16" thick and will cut through ferrous metal like a hot knife through butter
What is to prevent any decent welder from cutting those welds back off should the tractor need to be split for something else? And at that time installing a new ring gear (or new/used flywheel)?
If the ring gear has damaged teeth then the Only way it can be repaired is to split the tractor and install a new one.
If the ring gear is good but only slipping then a reliable and inexpensive way to repair it is to weld it.
See photo below.
About 6 years ago I bought a decent little 8N for $900 because the ring gear was bad. The guy I bought it from had paid a guy about $500 to split the tractor and put a new clutch in it because the ring gear was slipping.
The new ring gear also slipped so he threw in the towel and sold it.
I assumed the flywheel was bad - if two ring gears were slipping.
So I had my neighbor carefully hold the ground on the bolt on the front of the crankshaft and welded the ring gear to the flywheel through the starter hole in 4 approximately equidistant places.
The whole process - R&R the starter and welding took less than an hour.
Then I bolted the hood on properly and installed a used grill I had.
I put $25 worth of gas in it and bought my neighbor a case of beer.
Then I sold the tractor to a guy I know for $1500. A tidy profit. I know that tractor is still running today because I see it/him when I go up to my land.
I am entirely confident my repair will last as long as the new clutch will.
You may fix your tractor as you see fit. I will fix tractors as I see fit and not fritter away my time on things that do not need it.