Sorry it has taken so long to reply to the questions and comments, life has kept me away from the pc for all but brief moments.
So thanks Willkie, I'd heard about the poor selling hair but didn't know that was why those caps were made that way. People still do sell hair for wig making, I enquired about this a few years ago and found out that wig makers don't like hair from western cultures due to the use of hair products. As it happens I was lucky there as 17/18 years ago I was losing mine ( not male pattern but alepecia ) and it wasn't disease, diet or stress. So after trying various potions I just stopped using anything but water on my hair. In a couple of weeks the third of my scalp which had been bald was covered in small hairs. Dandruff and split ends , which had been lifelong conditions vanished at the same time, nor, after the first month, has my hair ever been too greasy or too dry ( previously it was one or the other most of the time). Personal opinion is that hair products are a scam, if you've used one recently and want ok looking hair tomorrow you have to use it again. Might be a lot of money in a counter scam if one was dishonest: sell pure water in bottles, say on the label that one must use nothing else for a month except ( if a few days of being too greasy is too much to cope with ) a bit of plain talcum powder to soak it up which is then brushed and rinsed out, and a lot of brushing if it is too dry. In a couple of months one would have hundreds of testimonials from delighted customers. I don't know if whether hair is treated or not makes much difference to it's strength for slings, a hair dresser told me that what most treatments do is strip out the natural grease and then coat it in plastic, may even be better for all I know. If it works for the spinning jumper making barber it would probably work for slings.
For pet owners dog hair looks like a good alternative anyway, there is a thread on this site with a link about it
http://slinging.org/forum/YaBB.pl?num=1142703081/10#10. Here in the UK this is the time most dogs are moulting. As to how long the hairs have to be Wanderer I've found various answers in various places, other people on this site could give a better answer than I can. However as far as actually putting the thing together goes not very long at all. Spinning is such an ancient and continuous tradition that it is full of terminology, wouldn't be surprised to find words related to spinning mammoth hair sometime. One of these terms may help answer your question. When spinning the bit from the top of the stuff you have twisted to the bit where the fibres have been drawn out but are not yet twisted, the place where the fibres combine would be another way of saying it, is called the drafting zone or cone ( for me it wasn't a cone but flattened ). I think that one would have to be very skilled to use fibers longer than the drafting zone with a drop spindle. ( I'm sure it could be done though either with skill or cleverly designed equipment). I'd guess no shorter than that would give a desirable minimum, so can't say in units of length as it would depend on dexterity. Another factor is probably how many turns a fibre has in a given twist, too few and it may spring out.
The Victorian were a strange bunch in some ways, their melodramas were nearly as simplified, predictable and emotionally extreme as our own TV/film fiction but for them grief, sorrow, frustrated undying love and bereavement were the big hits rather than anger lust and ego pumping fantasies, perhaps it was something to do with the Queens perpetual mourning after the death of Albert. I've seen some of those memento mori and it is odd. To some extent deep mourning was a fashion. D G Rossetti wrote some poems for his sister, Christina, when she died and put the only copies in her coffin as they were for her alone. A few years later he had her exhumed to get them back. I don't recommend graveyards as a source for hair, that really would be yerrrhhgh.
Ah the ruler, well it is an old school ruler, one can also make out the name of the a band we were into at the time, it was all I had to hand when I took the photo, couldn't use the other side of it as it has names scrawled over it. Truth is I can't remember... but you can't have a ruler without rules so don't worry about it, in the great scheme of slings it's neither hair nor there.