I'm not a machinist, but I'm with Kevin on this one. I wouldn't use that spindle either. Your best bet may be to find a complete axle. The dimensions (track width, spring perch width, drop, etc.) are identical through many years. The only thing that really changed (other than later years being beefier axles) was kingpin diameters, and two of the mounting holes in the spindles on later axles (forget what year) were 1/2" instead of 7/16th. Easy enough to drill your backing plates. I see axles popping up on Facebook Marketplace every now and then.
If you don't find something, maybe call Sid. He always has cores ready to be dropped, as well as spindles. Perhaps you could talk him into selling you a core. He'd probably even check it to make sure everything is in spec, or do any other prep work (kingpin resize, install, etc) you may need, but of course you'd have to call to ask.
Here is a handy link. You can scroll down to see all the specs for all the axles through the years. I have a '50 axle from Sid on my '36. I went with the later axle for the bigger kingpins.
https://droppedaxles.com/chevy-dropped-axles-0
