Originally Posted by
paulb_in_bkln
It seems to me it's the seat tube angle that is the main, more difficult to duplicate, difference between your Rudge Aero and one of the many easy-to-find DB steel frames that would make good platforms for one of the more unusual old SA hubs, like the FW.
Yes, I think that's correct that the frame angle cannot be duplicated
But at the same time, the effect of seat tube angle is setback of the seat tube lug from the BB plumbline. That added setback, measured at teh saddle, can be compensated with a seatpost that has a higher setback.
So while you can't duplicate the ST angle, you can achieve similar setback by using a deep-setback seat post such as a Nitto S-84 or one of the lower cost high-setback posts.