Originally Posted by Hondo6

Magnet should tell you immediately if the rims are steel, unless they're extremely unusual and made from some nonmagnetic stainless steel alloy. (I don't know if the latter were ever made, but it's at least a theoretical possibility.)

700c tires will not work on rims made for 27 x 1 1/4 or 1/1/8" tires. 27" tires actually have a larger bead seat diameter (630mm vice 622mm) than 700c tires.