sürece is a conjunction which is typically used for creating adverbial clauses. (If you translated that sentence into English there would also be a subordinating conjunction like until in the sentence - in the Turkish sentence DIK represents that subordination.)

If it was için everyone would say it is a conjunction.

I have checked again what a conjuction is: here

I don´t think "sürece" is conjunction here. I cannot see the bits connected by it. As I said earlier, it is not used without -diği suffix. It doesn´t connect 2 words, sentences, phrases or clauses. It´s a part of a clause which functions as adverb.

-ce suffix can be used to make adverbs of time and measure

2 gün boyun-ca = for (a period of) 2 days

2 km boyun-ca = along (a way of) 2 kms

günler-ce = for (some) days

metreler-ce = along (many) meters

süre=period

 with -diği; it is modified by adjective clauses:

yaşa-dığım süre = the period I have lived (so far)

The clause is treated as a unit and -ce suffix is added with the above mentined meaning:

yaşa-dığım süre-ce = for the period (or as long as) I have lived (so far)

subclause can be longer still it should be treated as a unit:

köyde yoksulluk içinde yaşa-dığım süre-ce = for/during the period (or as long as) I lived in poverty in the village

As a whole, it´s an adverb so it is adverbial clause.

Daha önceki çalışmaları incelemedikleri sürece iyi bir proje hazırlamaları imkansız görünüyor.

The bits connected by sürece are

                  "Daha önceki çalışmaları incelemiyorlar"

                                      AND

                  "iyi bir proje hazırlamaları imkansız görünüyor".

Two sentences, the first one is subordinate to the other (and thus marked with DIK). What defines its syntactic and semantic position in accordance with the main clause is the conjunction sürece.

It changes into an adverbial clause, yes yes, but the inner structure of the clause is this.

Makes very much sense. Probably this is how it came into being.

http://www.hemeningilizce.com/ingilizce-ders/zaman-baglaclari-2

They say it is a conjunction.

They only say so. I have provided some analysis above. If you point out anything wrong with it maybe we can further talk about it.

I am too old for such an argument. I can only copy and paste

I love such arguments.

why we use to say I am too old for  something and never I am too young for this...

I am  too young to drive a car.

I am too young to die.

http://www.youtube.com/watch?v=nJXlrI8proI