I finally got around to doing my spring straps. Thanks for all the good info here.
McMaster Carr has changed the part number on the springs, and you can now buy in quanities of one.
The new number is 3932K54 for a Long Type 302 SS Extension Spring 11" length, 1/2" diameter OD, .062" wire diameter. My springs were really only 10 1/2" long, I guess they measure them before forming the loops! $4.42 each.
I also purchased the shackles from them, they do have a less expensive SS model. It is Type 316 SS Cast Anchor Shackle with screw pin,3/16" and the number is 35355T13, cost $3.00 each. The screw pin is 10-32 thread, so that would be the size needed to replace it with a SS machine screw.
I have mine assembled and will "Test Dive" them tomorrow.
Mike