OLD Cisco routers - 4K

Hi !  I work for a company that wants the world for nothing - but then don't we all !!!!!!
I have been asked to set up a test lab consisting of 3 "sites" with full mesh WAN connectivity at no cost (!).  I have asked some people for some Cisco kit to build the design but the only kit I have been offered is a number of Cisco 4k routers.  I have double-checked with the people in question and they confirm that they are very old Cisco 4k routers - and not Catalyst 4k's.
My question is - is there anyone there in EE-land that has ever worked/configured these beasts ?  What IOS version can I fit on them ????????  I had a look around the Cisco website and the oracle known as Google and I can't get any info of any use.........any help appreciated.
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-Leo-Connect With a Mentor Commented:

This is a link to cisco webpage regarding 4000 routers. Click on the "Documentation" link and this will bring you to the right place!

They are really old but they do their job ...
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