nswsailor said..Cisco you said,
"I am going to have heavy iron blocks with a bar around which I will loop a mooring line."
Surely you mean your anchor line will have a gal thimble and a large gal shackle onto the bar?
Otherwise that rope is not going to last long!

The mooring line will have a spliced eye with plastic hose on it for anti chafe. The eye will pass under the bar and the mooring line passed back through the eye and cinched up tight.
Midtown Marina's commercial moorings were originally chain but they were only getting three years out of them. They changed to all rope and end of problem.
The water flow in the river causes electrolysis which just eroded the chain away. I have bought top quality "Super Dan" rope which is more than twice the strength of equivalent size "Silver" rope.
Based on other people's experience I am confident with what I am setting up.