Knocked it out the park on your first build; kudos!
Keep it as is; looks fantastic, and if it rides as good as it looks, why mess with it. I would swap out the syncros seat post before installing a syncros stem on this build.
Regarding fitting; why a 19" team comp, but a seemingly much smaller more modern Merlin frame:
Geometry and Effective top tube would be my guess. The Team Comp does not have any slope in it's top tube, so the actual top tube is also the effective, plus the angle of the headtube and the seattube, give you a tighter cabin. While the Merlin has a slope in the tt, and a more aggressive geometry, making the effective top tube the more meaningful measurement, than the frame size. I wouldn't be surprised if the effective top tube was somewhere in the same range as the actual top tube of the Ritchey, thereby, giving you your comfort level with the two.
Perhaps I'm off here; if so, I'd love to read why I'm off, and what would it really be instead
One more time- Bike of the Month for September; nicely done; Rocco