Pistons, Rods, and Cranks

In addition to all the different compression ratios, bore sizes, etc. there is one strange difference between flathead pistons.  I do not know the years each kind was used - any information would be great!  It appears that Ford added a 4th ring low on the piston to help stabilize the piston in the bore.
The rods do not use rod bolts.  Instead, the main part of the rod has machined threads.  The rod cap is held in place by castle nuts on these threads.

Here's a shot showing the whole 1947 rotating assembly.

The main bearing caps have a unique way of attaching to the block.  Note the curved slot in the block to take the raised area of the main cap.

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