Jay:
Thank you for giving me some mental exercise. From Spokecalc I determined that for Campy high flange hubs and Ambrosia Elite 27x1 1/4 rims (Spokecalc didn't list the Elite 19 rims in 700 C) strung 3-cross the length was: Front: 295.5 mm Rear: 295.4 mm left side, 294.5 mm right side
As a cross check, I used my 4th Edition Sutherland's. (the red one), Sutherland's chart calucated 294 mm for 27 by 1 1/4 and 290 for 700 C.
As I have found Sutherland's chart to be a tad short, I think you should use 295mm or 296mm for 27 inch wheels,, and 291 or 292 spokes for 700 C wheels.
To use Sutherland's, first find the chart for the size wheels you are using. In this case it gave 300mm for Campy High Flange, Then you find the correction factor for the rims you plan to use. For Amborsia 19 with single eyelets the factors were -6 for 27, inch and -10 for 700C.
Hope this helps.
Steven Snider
steve.snider@comcast.net