If you are trying to imitate a 1970's bike, here are some 'faithful' modern clone rims that are still available at retail.
Alex X-404 ~ this is very much like the weinmann single-wall alesa rim, but lacks the dimples of the 1960's model. Basically, single-wall ~550gm+ with a hump in the profile (Alex hump is smaller than weinmann hump) :
http://www.yellowjersey.org/
Weinmann made an undimpled late-1970's model (I have some of those NOS in my garage). I think the nashbar budget 27" rim is the Alex X-404 rim, or a close cousin.
Weinmann RM-19 / 219 ~ these are still available, in some shops and through some outlets (maybe niagara cycle works on amazon, maybe as full wheels.) They are a vintage rim, although these ones are 'made in USA', not 'made in belgium'. They are single-wall with a mesa (rather than a hump) in the profile. A more narrow (maybe 15mm) version was shipped on Raleigh Super Course MK2's 1974-76.
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Among modern rims, I think the M13-II is probably the lightest and nicest polished 27" rim, although the sources are probably getting scarce by now (again, maybe Amazon / niagara / bikepartsusa). Some shops like yellow jersey will also link you to national wholesalers that are still showing stock in the Weinmann 219/RM-19 and M13-II rims.
- Don Gillies
San Diego, CA