Can any one guess what he is making?

Fixture to hold pistons in milling machine so they can be milled or valve pockets flycut, very impressive work! Those look like piston pins in the heim bearings, so that's my guess...
No. The diameter of the pin you are looking at is 1 3/4" The reason I know that is I just got two 1 3/4 Fenner locks in the mail.

That pin that is through at an angle is just a test to see the angle travel for interference. He is setting it up to use on the 58 inch mill table it is on. But he will need a 8 x 18 inch riser for the head to increase table to spindle hieght.

He bought this rotating 24 " table to make a riser for the series II. he is ordering a piece of 18" diameter x 2" wall seamless cold roll pipe to make the spacer. The table is setting on the craftsman tool box. That table has to weigh every bit of 400 lbs

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