But it's so much fun to speculate. Here's an article on comparing steel wheels with Centerline Convo Pro, which I suspect is as light a wheel as you will find:
Light Wheels Vs Heavy Wheels - Wheel Tech - Comparison - Car Craft
Considering only the front, the weights:
M/T E.T. Front 26x4.5-15 11.42lb
Convo Pro Aluminum 15x4 9.64lb
Rally Steel 15x4 18.78lb
The rear Centerlines:
Convo Pro Aluminum 15x7 11.13lb
Convo Pro Aluminum 15x8 12.43lb
The weight of a 4x19 Centerline, if it existed would be about 11-12lb.
Another way to look at it is the aluminum wheel and the tire have similar weight, while the steel wheel is 50% greater. so it looks like on forged aluminum the weight would be nominal, but on steel the 19" tire combo would be heavier.
I'm pretty sure cars raced on aluminum wire wheels in the 30s, but you'd be paying museum prices. Can you lace an aluminum motorcycle rim on car spokes and hub?