Running backstay specifics

[mholmes]

I am planning on using amsteel (5/16" good?) to a block on the rail to the primary winches, as I have read recommended previously on the forum.

Can I use any standard block or do I need something seriously strong? Is there some reason why everybody always recommends a snatch block when it seems to me that a standard block does the same thing for a third the price? Same thing with the padeye? What loads are we talking about here?

and the most tricky question: how do I know how far back to locate it along the rail?

much thanks,
matt