Those are correct, one on each side under the frame rails. I believe all years had them.
There is also an additional long plastic shield probably 16" long on the drivers side under the frame well towards the starter. I don't have a picture handy at the moment.
Second line is:
PP (New Process the mfgr)
833 (4 spd manual trans)
3938 (10,000 day calendar, May 9, 1972)
028 (28th trans assembled that day)
First line should be the last 8 digits of the VIN, but that one looks strange.
1357951 looks ok except for the last "1" and the the model year and plant...
There is nothing that is welded. Three pieces - floor plate with a gasket which is bolted to the floor pan with three bolts, an o-ring, and the o-ring retainer which is bolted to the floor retainer with two bolts.
Looks like you are also missing the the plastic retainer between the column and...