This is GM Powerglide automatic transmission input shaft. This is an aftermarket shaft for high performance applications. I have included a couple of links that explain how this part evolved and why there are different designs of the same shaft. The URL showing the TCI brand shaft available from Summit Racing is very similar to yours but has an extra groove. These also come in different lengths depending on the other parts used inside the transmission One of the URL's explains this. Some shafts (like yours) have no grove on the torque convertor end of the spline. The maker of yours is unknown.

This is GM Powerglide automatic transmission input shaft. This is an aftermarket shaft for high performance applications. I have included a couple of links that explain how this part evolved and why there are different designs of the same shaft. The URL showing the TCI brand shaft available from Summit Racing is very similar to yours but has an extra groove. These also come in different lengths depending on the other parts used inside the transmission One of the URL's explains this. Some shafts (like yours) have no grove on the torque convertor end of the spline. The maker of yours is unknown.

References:

https://www.bteracing.com/news/posts/material-grades-and-designs-for

http://drr.infopop.cc/eve/forums/a/tpc/f/80760912/m/1857073186

https://www.summitracing.com/parts/tci-749602/overview/