Congratulations on the impending arrival.
My opinion is the #1 improvement to be made on a Gen. 1 for handling improvements is switching to front and rear radial tires. While 15" radial motorcycle tires aren't unobtainable as they were in the past, you won't find any in a V speed rating (to 149 mph, coincidentally the max speed usually listed for a Gen. 1). If you find yourself above double-digit speeds then radial tires will improve the confidence you have in your bike's handling, especially on less-than perfect pavement, and on curves.
You should be looking for a 17" or 18" rear, something in a 5-1/2" rear will fit between the swingarm. Anything wider will require swingarm widening. 17" rear radial tire has more rubber choices, but will cost you top-end speed, the 18" rear radial tire is a bit-shorter height to the OEM rear wheel tire combo, but will not cost you as-much top end.
You can use a OEM front wheel with a radial tire, don't go wider than the OEM size if you aren't widening the wheel, in the radial tire you fit. It's not optimal, but it can work. A 3-1/2" wide front tire/wheel is what's suggested for a radial tire to 'spread' its beads properly.
I offer 17" and 18" X 5-1/2" rear wheels on OEM splined hubs, a bolt-on swap. The first is an 18" wheel with a new billet rim bolted to a machined OEM splined hub.
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The 17" has a used rim welded-on an OEM splined hub. It's less-expensive.
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