Just as an aside. What dimension is the seatpost of your Ricardo?
I picked one up the other day of another forum member. It to is made from Tange 900.
All my other Ricardo's, built from tange 2 & 5 and Ishiwata tubing, have used a 26.6, 26.8 and 27.0mm posts. This one is really small and I have none that will fit. I think it's a 26.0 or 26.2. It would interesting to hear what yours is.