Seems an odd request, definitely needs more detail, unless you know your computers they were pretty bland to most observers.
To me there are three enclosure styles: the original monolithic white box, the later black box with colour accents and the current generic POWER rack style - none jump out as particularly photogenic. They came in many different sizes too, perhaps the greatest range of enclosure sizes for any single family(at least for the OS/400 V3 era)? They're really heavy too, heavy gauge steel was common. I see some of the black-with-colour-accent machines on eBay, be cheaper to buy one of those, or at least the plastic front skin. Or they could just make a copy of an IBM logo and stick it onto a bar fridge or an air-conditioner.
