Here is a few images of original pike heads. One caveat though, I'm not sure that these were dated correctly. They could date from the 14th century to the 18th, YMMV. The first set are Swiss (I know, boo hiss :) ) and are said to date to around 1500, although judging by the length of the langets they might date a bit later (1530's ?). Note: some of these images are very large.
You are quite right Thomas - that PDF is mostly halberds - my apologies! There is some information on the mounting of pikes included in the text sections, but most of the images have nothing to do with pikes, or deal with only the more unusual versions such as the “awl-pike”.
It's not a hard and fast rule, just something I have noticed. In general the langets appear to lengthen over the late 15th and early 16th centuries. At least if the woodcuts are to be believed. There are many exceptions though, so I just use it as a rule of thumb. By the end of the 16th century they are much smaller or disappear all together. Maybe because of the ascendency of the gun? I do know that by that time the big zweihänders had become a ceremonial instrument and were not used in war any more so maybe the need for langets was no longer necessary? You can see a similar development with the langets on halberds as well. It is interesting that the pike and halberd survived into the 17th century, but the zweihänder did not.
There is an article in the Journal "Waffen- und Kostümkunde" from 1909(?) which deals exclusively with pikes. It is a little dated ( ;-) but still quite useful imho. I´ll look up the citation until tomorrow.
Now I have made a major step backwards in the process. I spent six and a half hours in my car for NOTHING! I was going to pick up the wood for the shafts and had specified very clearly what I wanted. After looking through a hundred pieces I had found nothing even close to what I needed. I hate people saying they have what you need and then it turns out they have not got a clue on the subject.