Some thoughts:
1) Conrods are made from a variety of materials from forged steel to sintered metal so the suitability would depend a lot on what kind you can get.
2) The geometry of most modern conrods has a rather unfortunate aspect ratio if you try to use it as a cylinder. That is, the bore is very large compared to the height of the cylinder. As engines get more compact and lubricants and metallurgy get better this situation will get worse.
3) The big end of every automotive conrod that I've ever seen is split into two parts which greatly reduces its utility for your purposes since, usually, there are bearing locating features at the parting line between the two parts which interrupt the cylindrical surface.
So, if a conrod was the last piece of metal on earth you might get some kind of cylinder from it, but there are far easier ways (IMHO).