Are you sure what size you need? There is a big difference in sizing between older steel frames and modern ones - just because you ride a modern size 54, doesn't mean you need a 54cm in older steel (My "modern" carbon bike is a 54cm pinarello, yet all my older bikes are 58 or 59 cm C-C). And even just among modern bikes not all size 54 frames from different manufacturers are the same size, depending on how the measure them there can be large differences between frames that are of the "same" size. If you go with a smaller retro frame because you want plenty of seatpost showing, you might find the TT is too short.
I see lots of nice retro bikes, but most are smaller than what I could ride!