The RRA was the high water mark for the kind of bike you're talking about. Incredibly light frame, awesome graphics, beautiful workmanship, and several proprietary parts(crank, pedals, bag support, stem) made specifically for this model. The stem was chromed steel, presumably 531, with a lug that matched the lugs on the bike frame. It was basically a deluxe version of a pre-war bike, obsolete before it hit the market.

i had one from 1948, and i liked the geometry so well that i copied it when i had a custom frame made. I loved that RRA too much, always wished I had the correct crank, among other things. I had to sell it before it became an obsession.

The RRA frame weighed 72 ounces. 531 frames in my size typically run 75-80 ounces. My two A&P frames are even lighter- Fothergill is 69 oz, Armstrong 68 oz.

As was mentioned yes, I have an Allegro. It came from John's bike shop (Pasadena?) and lived a hard life in the salty fog of San Francisco Bay. It's a 1960 with all the best components of that era.

The Allegro and the RRA were as different as 531 bikes could be.

The Allegro frame weighs 80 oz.