A few links to try:
North American M-Scow Association: Sailing Hints I
I don't quickly see running rigging lengths, and that's may be, in part, because the owners and different manufacturers modify the rigs so there isn't really a standard.
A rough guesstimate for the main halyard is twice the height of your mast plus 2-3 feet, depending on where it cleats.
The jib halyard is going to need to be height of your mast plus the length of the forestay, plus at least 2-3 feet depending on where it cleats. If it's hard to measure the length of the forestay, you can probably get away with twice the height of the mast plus 4-5'. The way a right-angle triangle works out, the longest line, which would be your forestay, is pretty close to the length of the longest side if one side is significantly longer than the other, as is the case with most boats.
Once you're able to hoist the sails, then you can buy cheap rope from Harbor Freight, Home Depot, etc. and figure out the other lengths. For example, for the jib sheets, assuming you are dead downwind, which is about as far out as the jib will get, the lazy jib sheet will need to be the longest. There, I think it needs to be length of the foot of the sail plus the beam of the boat plus a few feet. In this case, I'd probably over-order by a few feet each way, unless you want to actually fly the jib with the junk rope to get the "right" measurements.
The vang and main sheets will depend on the hardware you have. Again, I think you're better off using cheap rope to take the measurements.