Originally Posted by T-Mar
If you've got the necessary reach with your brake pads, you're better off going the 700C route for all the reasons stated by Repechage. However, if 27" is your only option, I'd suggest the Sun CR-18, which is still made in a 27" version. I.m not sute about the weight, but it is aluminum and of box-section/double wall construction for extra durability. About a month ago, I installed one for a 300 lb riding who flat spotting his normal U-section Arayas. So far, there has been no reported problems.
+1 on the Sun Cr18 rims. I just did a converison where I switched from 27" to 700cc and am using the Sun rims and 32mm Schwalbe Marathon tires for a vintage, road style commuter bike. Very happy with the set up. Also going to 700cc will allow you to run studded tires if winter riding is a part of your plans. There are no availble 27" studded tires unless you manke them yourself. I can run the 35mm Nokian studded tires w/ full SKS fenders. The older bikes have much more flexibilty with regard to tire clearance.
Good luck!