Those look homemade to me. Years ago, when I was vintage dirt racing, Speedway Motors offered wheel shells and wide five centers, and I was able to make my own wheels with custom widths and offsets. Those centers look a lot like the centers sold by Speedway. Also, a close look will show that the welds are a little more crude than commercially produced wheels.
EDIT : Here's the listing for the center :
https://www.speedwaymotors.com/Wide-5-Wheel-Center-for-15-Inch-Steel-Wheels,7403.html.
I see they are "No longer available".