A grinder to cut cable will change the metalurgy enough that you may have rust bleeding in/around the fitting unless you "pickle" the cut with an acid paste, available at welding supply. There is no time savings over a good old hacksaw with the best blade you can find (bimetal or hi-zoot). An improvement for the hacksaw (mentioned here earlier) is to drill a 2 X 4 (hole is wire size), slip the wire in the hole and cut it through the wood lengthwise, using the wood as a guide.
To leave a mast standing while fitting wire lengths it should be supported by four points, either uppers or lowers.. your choice. This can be accomplished utilizing strops & handy billys. In this way you can position the mast, plumb athwrtships & proper rake, in order to get the wire lengths correct.
It sounds like fun, I wish I was there to help
Cheers, Russ