Halloween, stature, pre-celtic...

I started with this google search (just paste it in as a URL to recreate the result set):

http://www.google.com/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&q=celtic+folklore+%22little+people%22+halloween

Some possibly-useful results:

http://www.tylwythteg.com/Hallow.html
http://www.mythinglinks.org/Samhain.html
http://www.bbc.co.uk/dna/h2g2/alabaster/A175385
http://216.239.53.100/search?q=cache:yaouMrcPWnYC:www.belinus.co.uk/folklore/CelticFolklore/CelticFolklore42.htm+%22pre-celtic%22+folklore+halloween&hl=en&ie=UTF-8
http://www.cyberfae.com/library/eb_ffcc240.html

http://perso.wanadoo.es/selicup/G2manuelalberro.htm
from: http://users.pandora.be/diogenes/kelten2.html

The oldest archaeological evidence of the Celts comes from Hallstatt, Austria, near Salzburg. Excavated graves of chieftains there, dating from about 700 BC, exhibit an Iron Age culture (one of the first in Europe) which received in Greek trade such luxury items as bronze and pottery vessels. It would appear that these wealthy Celts, based from Bavaria to Bohemia, controlled trade routes along the river systems of the Rhône, Seine, Rhine, and Danube and were the predominant and unifying element among the Celts. In their westward movement the Hallstatt warriors overran Celtic peoples of their own kind, incidentally introducing the use of iron, one of the reasons for their own overlordship.

For the centuries after the establishment of trade with the Greeks, the archaeology of the Celts can be followed with greater precision. By the mid-5th century BC the La Tène culture, with its distinctive art style of abstract geometric designs and stylized bird and animal forms, had begun to emerge among the Celts centred on the middle Rhine, where trade with the Etruscans of central Italy, rather than with the Greeks, was now becoming predominant. Between the 5th and 1st centuries BC the La Tène culture accompanied the migrations of Celtic tribes into eastern Europe and westward into the British Isles.

http://www.paganism.com/ag/articles/fairy-faith.html
from http://www.jrbooksonline.com/HTML-docs/Phoenician_Origin_ch12.htm

At the outset we are confronted by the paradox that, while philologists and popular writers generally in this country assume that the "Celts" were Aryans in race as well as in language, and were the parents of the Brythons or Britons, and the Scots and Irish—notwithstanding that the "Early Britons" are also called non-Aryan pre-Celtic aborigines—on the other hand, scientific anthropologists and classic historians have proved that the "Celts" of history were the non-Aryan, round-headed, darkish, small-statured race of south Germany and Switzerland, and that "Celts" properly so-called are "totally lacking in the British Isles." {But see later.} Thus, to speak, as is so commonly done, of "Celtic ancestry," the "Celtic temperament" and "Celtic fire" amongst any section of the natives of these islands, is, according to anthropologists, merely imaginary!

The term "Celt" or "Kelt" is entirely unknown as the designation of any race or racial element or language in the British Isles, until arbitrarily introduced there a few generations ago. Nor does the name even exist in the so-called "Celtic" languages, the Gaelic, Welsh and Irish. It is, on the contrary, the classic Greek and Latin title of a totally different race of a totally different physical type from that of the British Isles, and that word was only introduced there by unscientific philologists and ethnologists some decades ago.

The "Celts" or "Kelts" first appear in history, under that name, in the pages of Herodotus (480-408 B.C.). He calls them "Kelt-oi" and locates them on the continent of Western Europe.

http://www.faqs.org/faqs/cultures/celtic/celtic-faq/
http://libro.uca.edu/stanislawski/Chap5.htm

Some from a JSTOR search for "pre-celtic and stature":

The Ancient Peoples of Ireland and Scotland Considered Hector MacLean
Journal of the Anthropological Institute of Great Britain and Ireland, Vol. 20. (1891), pp. 154-179)

An Anthropological Study of Eastern Shropshire and South-Western Cheshire: Abo Blood-Groups I. Morgan Watkin
Man, New Series, Vol. 1, No. 3. (Sep., 1966), pp. 375-385.)

...and this one is 130 pages, too much to grab the .pdf:

Geographical Distribution of Anthropological Types in Wales.
H. J. Fleure; T. C. James
Journal of the Royal Anthropological Institute of Great Britain and Ireland, Vol. 46. (Jan. - Jun., 1916), pp. 35-153.

Not many books that I can find that directly address 'pre-celtic', but one is:

Macalister, Robert Alexander Stewart, 1870-1950.
Ireland in pre-Celtic times.
Published : [New York] B. Blom [1970]

Good old google surely does have a lot of 'pre-celtic' pointers, perhaps worth pawing through:
http://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=pre-celtic