Are you having a new chassis built? If so, you don’t need this alignment bar. A new chassis is usually set up with a bar attached to the 3rd member or housing and passing through the main bearing bores of the engine block. This provides a perfect alignment from engine/trans to the rear end.
However, if you buy a used chassis and plan an engine change, new mounts or the installation of a mid-plate, this bar will help with the alignment process.
In this case, the bar is attached to a coupler with a Powerglide spline. The aluminum piece seen in the picture adapts the coupler to the bar. The front piece can be anything round like a yoke with the u-joint portion cut off. Something that fits snugly in the back of the transmission. Another option is to make an adapter that fits snugly over the crank flange with the indicating bar attached. There are many options.
The length of the bar can be shortened or lengthened for use with other applications.
As seen in the second picture, the indicator is attached to the end of the bar via aluminum adapter and set screws. If the length of the bar is changed, the adapter can be re-inserted in the bar as the set screws for the indicator also hold the adapter in place.
If this is of interest to you, give me a call or email me at firstname.lastname@example.org. The cost will be about $200 less indicator.
There is one assumption to consider. That assumption is that the original setup placed the engine in the correct alignment with the rear end. This bar will ensure correct placement in respect to the pinion.