GL - yes I was thinking that those lengths would be important also. I'll play around with some extra line, tie the loop on, and then give myself an extra inch or two as the target length.
The diamond knot looks the hardest to do. I saw mentioned on a couple of sites that the knot is the point where the shackle will fail, if it is going to fail. Makes sense.
Yes Polypropylene, I had that wrong. It may look knobby and rough, but the 9mm Regatta Lite feels SO smooth in my hand, and SO light. Also have some 8mm Bzzz line that I may use for the jib sheet... so a shackle that will work with either 8 or 9mm.
Thanks!