I've used the Harken Ratchamatic blocks on the jib of my Tornado for 3 years with no problem. Mark the little arrows, that tell which way the lines run, in red. It will cut down on the number of times you put them on backwards.

As far as cutting the cover off your main sheet, I have what I think is a better way.

For the mainsheet use a line with braided hollow core for the core. That way you can pull the core out a little and splice spec 12 to it for the taper. The splice is a hollow core to hollow core which even I can do. The splice is almost the same diameter as the original line so it runs smooth. When the taper gets worn, cut it away and splice on more